If a child is bored, stressed, or even just falling asleep, he may rock himself back and forth or bang his head. This can worry parents, and may even damage cribs, but rocking and head banging can be normal. Children with more intense personalities will rock and bang more than others. These habits can begin around 6 months and continue into adulthood.
There are some real problems that can cause rocking and banging, including:
If your child rocks or bangs his head, he should get a careful physical exam to rule these causes. If none of these causes is found, you may want to make heavy rocking part of your nightly routine. You may also want to bolt the crib to the wall.
Make sure that your child is not being put to bed too early, and therefore spending time in the crib awake and bored. If this is the case, try putting your child to bed later, when she is showing clear signs of sleepiness.