Roughly 7 percent of 3-year-olds are sleep-deprived, getting less than 10 hours of sleep a day, due partly to parents coming home from work later than before, according to a government study.

The Environment Ministry study covering more than 100,000 children also found that about 29 percent of 3-year-olds were put to bed at 10 p.m. or later, as were around 13 percent of 1-year-olds and 16 percent of 18-month-olds.

It is generally considered appropriate for children aged 3 to 5 to sleep 10 to 13 hours a day, including naps. The study found that about 44 percent of the 3-year-olds averaged 10 to nearly 12 hours of sleep, 47 percent 12 to less than 14 hours, and 2 percent 14 hours or more.

The study also showed that 2 percent of 1-month-olds and 3 percent of 1-year-olds average less than 10 hours of sleep a day.

For the study, the Japan Environment and Children's Study polled mothers of more than 100,000 children born in 2011 or later.

The tendency for children to be put to bed later was greater among mothers aged 40 or older or under 20. Researchers at the University of Yamanashi who analyzed the results said the higher figure for older parents may be due to the presence of older children.

"Japanese babies have shorter sleeping hours when compared internationally," said University of Yamanashi professor Zentaro Yamagata, adding he hopes to continue studying how sleep deprivation in early childhood affects later development.

The study results will be presented Saturday at a symposium at the National Museum of Emerging Science and Innovation in Tokyo.