A new study is casting doubt on how parents should lay their babies down to sleep.
In the past, doctors have said newborns should be laid on their backs, to prevent sudden infant death syndrome.
Although this practice can save a baby's life, in some cases, it can also increase chances of flattening the child's skull.
To prevent that, some parents are using helmets custom-fitted to a baby's head, with the hope that it will help the child's skull grow in the right shape while they're sleeping.
However, new research says the helmet has virtually no effect in most cases.