You could have a movie Party. Set up a consession stand, give them fake money to buy treats, dress up at the person who works there, and take thier tickets. Get those small plastic popcorn boxes fromTarget , set up rows of seat in the movie room. Party favors can be bag of popcorn, and $5 gift certificates to Cinemark.
Bubble Party. Get some ballons and bubble wrap. Pick a room, move out the furniture, or push to the side. Line the whole room with bubble wrap and fill it with ballons. Enter boys. Unimaginable fun. We did this once, it was so simple, I wasn't sure it would work, but they had a freakin blast! They loved popin gthe bubble wrap, sliding on it, and throwing up the hundreds of ballons. It does take a lot of breath out of you, lol, and it's time consuming to set up that many ballons, but it was so funny to watch my 6 year old boys going crazy like a cat with catnip! As a cool off, watch Up while you serve them a treat. We made a craft too, paper mache hot air ballons. Do this in the same room after everythings been popped, that way the mess can just be rolled up in the layers of bubble wrap and tossed. Easy clean up.
Indoor "camp out". Not a sleep over, but you could do it in the day and black out the windows with long black paper from Teacher's Tools, Or have a late party, where they stay from 8-11pm. HAve them come in camp clothes, or jammies. Set up tents in a big room. (small tents at Ikea for $9)
have sleeping bags, or have them bring. Get mini flashlights for them. Set up a fake fire, usuing construction paper and real branches or cardboard. OR use yoru fireplace. Roast marshmellows and hot dogs over a grill or stove. scatter fake bugs all ove rthe place, download a nature ambiance cd to play softly in thebackground. Tell child appropriate ghost stories tot he kids. HAve them play games that are camp themed, you can goggle some. I found a list once, although I can't remember where. Make camp crafts. Gift bags could include a mini compass, mini flasjlight, mini bug net. trail mix.
Good Luck!