Yes. It's pretty easy to figure.
Kids are not free. All party members (adults and children 3 - 9) pay child prices for the dining plan and the tickets.
Get your room price, add up the ticket costs using child prices for the type of tickets you want, and add up the child DP costs with the DP that is attached to your resort tier (value = QSDP, mod =
DDP, deluxe = DDP) and that will give you the rough amount before taxes. If you upgrade your dining plan you'll pay the regular upgrade price (the difference between the adult QSDP to the adult DDP).
HTH!