L.D.
If you have a lot of people and a small house or appartment, try local parks. I know Richardson and Plano residents can reserve a covered picnic area of any park of the city for free, though you might want to plan ahead to have the first choice of location and date.
If you don't have time for cooking, fruits, healthy munch such as cut pita bread and humus, baby carrots, salad, cold sandwiches would do. Games for kids could be balls, water balloons, bike race with obstacles, running race.
You don't need to spend a lot of money to have a great party. Organization is more important in my opinion.
Good luck.
QA