Definitely adult products. My kids are 6 and 8 now. Have long beautiful hair but also needs de tangling in the shower.the kids shampoo just arent cutting it for us anymore.

I’ve responded to this on the other double up of this question- use what your child needs

About 2-3 . When their hair really thickens up.

I think it depends on the type of hair the child has. My toddler has very fine strands but a lot of hair. If I brush it morning and night it’s easy to maintain. I’ll use kids hair products as long as it’s manageable for his hair

Around age two for me.
My middle daughter had mega long hair and I used to buy hair detangling spray for her also.