The 19th-century lullaby "Rock-a-bye baby, in the tree top," hardly promotes a peaceful night's rest when it tells a child to expect that the wind will pick up, "and down will come baby, cradle and all."

It's a good thing we choose gentler tunes. (How about a collection of Beatles songs, all done as lullabies?) Children who don't hit the hay at (more or less) the same time every night and for the same number of hours often fall behind in reading, math and spatial awareness by age 7.

Irregular bedtimes disrupt body rhythms and undermine the brain's ability to take in and retain information. Three-year-olds seem most negatively affected. A study of 11,000 children found that kids at that age with poor sleep habits were the most disadvantaged intellectually in the first years of grade school. Erratic sleep patterns also trigger weight gain, difficulty controlling emotions and, suggest some doctors, the misdiagnosis of ADHD.

So if your toddler or preschooler isn't following a regular sleep schedule, here's what you can do:

1. Let your child get lots of physical exercise daily. It's vital for mental and physical health, plus it promotes sleep!

2. Turn off the TV and all handheld devices at least two hours before bedtime, and keep all such devices out of your child's sleeping area.

3. Set a "heading to sleep" routine: Take a bath; put on PJs; read books; then lights out.

4. Encourage your child to sleep in his/her own bed; it also promotes good sleep patterns.