Cats sometimes behave very unpredictably around babies. It can sometimes be funny, or very very stressful. When my niece was 1 year old, my male cat would often punch her in the head of she got too close. After being punched, my niece would start giggling, which made the situation even funnier. We’re pretty sure he was just playing (and it was pretty funny to watch), but we had to watch him very closely to make sure everyone was safe
Here’s a funny video of a kitten playing with a baby:
Warning: Do not leave a cat and a baby together unattended. You can never predict how a cat will behave, especially in your absence. In particular, some cats will lay on babies faces while they are sleeping. Your cat is not trying to kill your baby. Most likely, your baby’s head is warm and your cat is just looking for a warm place to sleep.