C.G.
Hello, for my kids we have done the indoor/outdoor amusment parks, chucky cheese's, swimming pool type parties all w/a sleep over. You could check w/your nearest pool & see what they do for parties. I don't know where you live, but there is probably an indoor/outdoor amusment park near by, the one we used had bumper boats, go karts & putt putt outside, inside was laser tag & all the games you find at Chucky Cheese's.
Then of course there are the home only parties: for the girls have them bring their make up & ribbons or bows so they can do each others hair & make-up & nails. Find the game dream date, a deck of uno cards. If you have a trampoline, they sell tents for them & they can sleep on the trampoline under the stars. Maybe have a bom fire & let them cook marshmellows (if you are out in the country).
For your son at home, camp out on the trampoline or in tents, a camp fire, have them bring their bikes for trick riding, send them on a scavenger hunt, have a baseball game, throw horse shoes, volly ball.
I don't know if this helps, but maybe you can use 1 or 2 of these ideas.
Good luck.