Hot beef sandwiches, you can get large quantities at Sams, or other grocery stores...mostly in the freezer section. Pasta salad, chips, fruit/veg tray.
You could also just do simple sandwiches (ham/cheese, turkey, roast beef, etc.) I am assuming its coming up soon or at least in the warm part of the year, do something that is light and quick...slow cooker meals are best. Either cub or Rainbow has pork tenderloin buy one get one free, normally eight dollars a piece, slow cook this all day, add bbq sauce and you have easy BBQ pork sandwiches.
Happy birthday to your little one.
You could also check out Chuck E cheese, I know, it sounds corny but they decorate for you, clean-up for you, etc. The games are only $25 cents each (tokens). YOu can buy a birthday package and its actually quite affordable when you break it down. You also dont have to worry about your house needing to be clean, and clean up.