Do you pay for everyone (or does each family pay for their own kid)?
この場合、次のような言い方ができますよ。
ーDo you pay for all the kids that you invite?
「招待した子供たちみんなの分を払うの?」
ーDo you pay for everyone (or does each family pay for their own kid)?
「みんなの分払うの、(それともそれぞれの家族が自分の子供の分を払うの)?」
ご参考まで!