High school students? I'm thinking Tivoli Woodfired Pizza in Utica (Van Dyke) or DaFrancesco Italian (spaghetti/lasagna) in Shelby Twp (Van Dyke). Neither place serves junk; I can attest. Both places would negotiate with you, unless you desperately approached them at the last minute. If your budget isn't bare-bones and your kids are "classy," you also may want to explore La Saj Lebanese near Lakeside Mall. Kids love kabobs and fried potatoes.
If you want to get yummy delivery to a public park, bounce me a reply and I'll help you arrange a good price from Louie's Pizza (with salad, etc.)--18Mile and Hayes, I think.
13776 Southcove Dr, Sterling Heights, MI 48313