K.H.
You should check out the rates of your county on the internet , it should all be listed into age categories and before/after school care. I used to look after a child after school for a friend & I used to drive to the school and collect her and also feed her and I was paid the county rate of $90/week. If you are in the situation that you don't need the money and would just like some extra pocket money for yourself then once you know the county rate why not deduct $10/week off of it? But as he has said he does not mind what he pays you then I would not worry about giving an amount , I imagine that he is just happy that his son is going to a friends rather than having a prolonged day in what is effectively school.