Try using mild baby hair oil which is chemical free and made of natural ingredients like Moms Co natural baby hair oil which is a combination of 10 powerful oil which helps to promote hair growth

My mom says use coconut oil but it makes by baby feel itchy. My baby had very less hair at the age of 6 months then I used mama earth nourishing baby hair oil. It is so good. It regrow my baby hair. And it smell so mild. It also don't leave baby head oil. It also works for the cradle. Crap. Or dandruff which is very common during summer to kids and babies.

You should do proper oiling it needs constant effort from your side to oil the babies hair properly also please check if you have changed any shampoo recently or if by mistake you had applied elders shampoo on baby's head do not change products so often for the baby