Since you have a boy that is into sports make it easy on yourself and throw and ESPN sports party at a local park. Do a basketball and flag football tournament and a bouncy and crafts station for any girls our younger kids present. Video tape the games and make copies to give to parents as a keepsake later.
1. BASKETBALL: Break the kids up into 4 or more teams and let them play games (on mutliple courts) to get to a championship game. You can even give each kid a medal for participation, or do some kind of small championship trophy.
2. Rent the jumper and set it up in the park as well for any girls that don't want to deal with the sports. They can also enjoy the playground at the park.
3. T-shirt/canvas bag design station for girls: This is another option where you have fabric paints and black t-shirts for the girls to design something for themselves.
4. If you have time you can also do a flag football tournament using the same logic as the basketball thing. There is a company called S&S that sells an entire flag football kit for a great price. Do a search online. Once again split into a few teams and play short 5 to 10 minute games and then a championship.
Best of luck.
Pam A