Venture Stories

Don’t Sleep on Sleep Training! Lullaby Teaches the Importance of Infant Sleep Health


Lullaby is a personalized sleep training service and platform for parents and their newborns.In this article, hear from founder Yukari Tago on how cultural differences and an unfortunate accident inspired her to create Lullaby. 

Key Learnings 

  • Different countries, different childbirth experiences 
  • An accidental wake-up call
  • Better sleep becomes more than a dream
  • Global effects of sleep deprivation

Yukari Tago, founder of Lullaby

Different countries, different childbirth experiences 

The launch of Lullaby was greatly influenced by my experience giving birth in the United States. While the procedures and preparations were more inconvenient and difficult than in Japan, I was surprised at the high level of child-rearing literacy that mothers had in the U.S.

Japan is safe and well insured. With an infant medical care card, you can receive free medical care throughout the country. But the situation is quite different in the United States.

One time I was at a friend of mine’s US-based home and I had noticed her thick medical dictionaries covered in sticky notes. She told me that she went through every detail of a recent doctor visit’s recommendation, such as whether there is a generic version of a recommended drug, if there is a cheaper alternative, what tests were recommended, etc. She even had suggested options that differed from her doctor's opinion! 

There were also differences in the birthing process. I had to choose the hospital where I would give birth and also make an appointment with an obstetrician that was covered under my medical insurance. Immediately after birth, I was assigned a pediatrician, and I needed to make an appointment with that doctor in advance. Making separate appointments for the hospital and the doctor was a big difference in itself, but I was indeed surprised when I asked an acquaintance for a hospital recommendation, he replied, "X hospital won't rip you off.”

Since I did not have many local acquaintances I decided on a hospital on my own after gathering information using classified websites and other resources. Other mothers I had met were so skilled in gathering such information, which was quite impressive to me. Also, in California, it was not unusual for mothers to return to work three months after childbirth, and it seemed normal for them to invest time and money in preparing for this.

One of the things I learned through my experience giving birth in the U.S. was sleep training, which helps babies develop the habit of falling asleep on their own rather than being put to sleep by co-sleeping or being held, as is typical in Japan. My obstetrician told me about the importance of sleep training and how proper sleep health, for both child and parent, is essential. After all, “you can't raise a healthy child if you are exhausted,” as she said.

I still wasn't sure whether or not to actually seek sleep training consulting, but an unforeseen event occurred when my child was six months old which drove my need for it.

An accidental wake-up call

My baby was continuously crying at night, leaving me so exhausted that it was hard for me to function throughout the day.

When my baby was six months old, he was still crying throughout the night, and I started noticing how constantly foggy my mind was during the day. One day, while he was sleeping on the couch, I took my eyes off of him for just a moment, but when he woke up he fell right off the couch. Had I not been sleep deprived, I probably would have kept a closer eye on him or noticed the moment he woke up.

Fortunately, it was nothing too serious. But I remember panicking and rushing to call a cab to take him to the hospital. I was terrified that I might have caused serious injuries. After that scary accident, I decided to seek consulting for sleep training.

"You can't raise a healthy child if you are exhausted.”

Better sleep becomes more than a dream

Before that incident, I had only considered sleep training. In California, where I had given birth, mothers often returned to work three months postpartum. It was common practice to work with a sleep consultant – a professional that handles sleep training and nighttime crying – to prepare a baby’s sleep environment, allowing the mother to return to work fully equipped to handle nighttime crying and sleep training on her own.

At the time I had been reading The Happiest Baby on the Block, a well-known book about parenting and increasing a baby’s sleep, since my son was three months old. But just reading about it didn’t really help the problem I was facing. I still wasn’t sure what to do.

The couch incident showed me that I had not been thinking clearly thanks to my baby’s continued night time crying and my own unwavering sleep deprivation. I decided to seek help right away. After receiving consultation and working on sleep training with my husband, I saw a change in my baby’s sleep pattern after just three days.

We would leave the room after putting my baby to sleep and watch him through the monitor to measure the time from the start of crying to the end of crying, and we would let him cry for about five minutes, then have contact with him for two minutes, and leave again for a short while, following a time chart. If I had been alone without my husband’s support, I would have broken down when I heard my baby crying.

The first few days were pretty rough but to my surprise he quickly began to adapt. After a few weeks, I was actually able to sleep through the night on my own as if by magic. I was so happy about it that when I shared it on Instagram, I was inundated with questions from my friends in Japan, "What is sleep training!?"

I received the same response from other people who used sleep training with their infants using the same method as I did. To this day, I still receive comments from users of the Lullaby app saying that they start to see changes in their infants after about the third day. Of course, there are individual differences, but that is the magic of sleep training! You can see improvement almost immediately.

For me, the change was drastic. I had read some papers with scientific evidence at the time, but I felt that perhaps if I had the knowledge, parenting would be much easier.

I was finally able to get more sleep and I even had enough time to myself that I could take night classes at UCLA Extension. Looking back, the first three to four months after giving birth are a hurdle for just about anyone looking to sleep train because it is a time when the baby does not yet have the strength to sleep through the night. With such knowledge, I would have felt more relaxed about the position I was in.

Global effects of sleep deprivation

Since my job was to develop new businesses in the EdTech industry, I had the opportunity to hear directly from CEOs and COOs about startups in Japan and overseas at the time. Perhaps that is where I was first attracted to the world of startups.

Later, I became pregnant in 2016, gave birth in 2017, took maternity leave, and returned to work in 2018. At that time, I particularly remembered the words of a senior employee at Mitsui & Co. who had started his own business. He said that when it comes to new businesses, it’s important to find a deep pain point. If it is deep, and if it is an issue that you want to solve no matter how much money you have to pay, it should be a viable business. 

Why Design Research Is Important in Building a Startup


After my son was born, for the first time in my life I was faced with the challenge of sleep deprivation. It was the most physically and mentally exhausting experience of my life so far, a true pain point.

While sleep training was a common solution in the U.S., it wasn’t in Japan. I thought, "This is it!" I continued to gather information to commercialize this idea. I later learned that Moon was going to hold its first pitch event, so I decided to apply. It seemed like a good opportunity. I pitched my idea for Lullaby and that was the start of my business to improve children's nighttime crying and improve parent’s own sleep.

Later, Dr. Mariko Morita, who participated in the project as a supervising physician, also found that the problems related to bedtime are significant.

According to data published by Ehime University in 2018, Japan ranks last when comparing the total length of sleep of three-year-olds in 17 major countries1.

But it's not just children’s sleep that is affected. Data published by the OECD in 2016 showed that Japanese adult males had the fourth-shortest total sleep duration of all 38 countries at the time (35 OECD member countries plus China, India, and South Africa), and adult females in Japan had the lowest sleep duration2.

Sleep deprivation is a major problem in Japan, and many people associate this to their feelings of anxiety about returning to work after parental leave, to fight because of frustration with their children not sleeping, to get divorced because their marriage deteriorates, or to suffer from postpartum depression. Although the methodology on how to improve this nighttime crying problem has not been established at all in Japan, there is evidence for the effectiveness of sleep training.

Out of 52 treatment studies from the American Academy of Sleep Medicine, 94% of the studies report that sleep training has been effective in improving nighttime crying, and more than 80% of children demonstrated significant improvement that was maintained for three-six months3. Even though the results are well documented, in Japan, there are no medical institutions or midwifery centers to provide guidance.

Research has shown that the rate of postpartum depression, stated to originally be about 15%, has increased to about 30% due to the impact of the coronavirus pandemic4, which may have a significant impact on mental health. And problems related to infant sleep contribute to the increased percentage as well.

I created Lullaby to help solve this very problem.


Lullaby is currently expanding its business domain by matching sleep consultants, providing reliable childcare information under the supervision of sleep medicine physicians, and developing other services such as general childcare consultation services.

The company has also begun joint development with Pigeon, and as of July 2023, plans to offer a "Nen-ne Kaizen Pack," which combines several services including the use of an application for local governments and the provision of sleep seminars for parents. Demonstration tests of the effectiveness of sleep improvement for families with infants and toddlers will begin sequentially in five municipalities: Kashiwabara City (Osaka Prefecture), Namegata City (Ibaraki Prefecture), Otsuki City (Yamanashi Prefecture), Gyoda City (Saitama Prefecture), and Morioka City (Iwate Prefecture). 


Check out the Lullaby website and Instagram for the latest information and updates!


*1 Health, Labour and Welfare Science Research Grants: Research Group on Sleep and Use of Information and Communication Devices by Preschool Children (ed.). Sleep guidelines for preschool children. Ehime: Sleep Medical Center, Ehime University Hospital, 2018.

*2 Average minutes per day spent sleeping in OECD countries plus China, India and South Africa by gender, as of 2016

*3 Behavioral treatment of bedtime problems and night wakings in infants and young children.

*4 Drastically increased postpartum depression during the COVID-19 pandemic and its association with social restrictions.

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