Hello, when can I start washing my kid's hair with shampoo.. my kid is 3.5 months old

A. From The day one itself whenever you bring your child home from the hospital and at home whenever you giving a bath to the child if you are giving a head bath to the child you can always start using shampoo from the day one it self there is no restriction on using any kind of soap or bar until unless there is some allergy to the child