If my child has a child, will I still be required to pay support after he turns 18?

Are you now obligated to pay child support until some time after he turns 18? I see no reason why that obligation would not continue.

It will depend on location and the terms of the child support agreement.

In some US states, the child is emancipated at the time they give birth, in many others they are not. Are they living with the custody parent still ?

Also at 18 many child support agreements end, what does your say