Question: When I put my 4-month-old son down to sleep, he shakes his head right and left pretty hard for a while and then falls to sleep. I think he's trying to get comfortable, but he shakes his head quite a bit. Is this a need for concern? —C.H., from e-mail

Answer: Head rocking isn't uncommon as a soothing technique or a way of quieting one's self when a baby is adjusting to a transition like going to sleep. It can be like thumbsucking or other soothing techniques.

With this kind of rocking, though, babies sometimes wear patches of hair off the backs of their heads in the process. Sleeping on their backs is difficult for active babies, who can more easily cuddle themselves and find their thumbs when lying on their bellies.

But our concern about the danger of SIDS (sudden infant death syndrome) makes it necessary to position babies this age on their backs, even though they then may resort to behaviors like this head rocking to soothe themselves.

When your baby is awake, you can prop him up at an angle at this age so he can look around and begin to reach for a safe toy strung across his crib. Don't leave him too much. Carry him with you or talk to him or play with him.

Are you worried about whether this head-rocking represents a neurological problem? It certainly needn't be, for many healthy young children do rock. If you're worried, check him out with his doctor and let him know your concern. He or she can look for other symptoms in order to reassure you.

Question: I have an 18-month-old child who is like a piranha. He bites 2-3 times a day at day care, and I dread the "Oh, no" reports I have to sign upon picking him up — not to mention the criticism I receive from the director because the other parents want my child kicked out of school. How can I get him to stop biting? Help! —C.K., address withheld

Answer: Biting is common at this age, but 2-3 times a day — on a regular basis — does sound excessive. It would be hard to blame the day-care staff and parents for being concerned about him.

Biting episodes usually occur when a toddler is losing control or getting too excited. He may not yet have learned to socialize, and biting is his way of engaging his peers and seeking attention, even if it's negative.