These mini quesadillas are best enjoyed while they're still warm - which gives your child the chance to play party host, walking around with a serving tray of savory appetizers he helped make. Don't forget a bowl of guacamole and a serving spoon so your guests can dip in style.
Heat the chicken, barbecue sauce, and onion together in a small saucepan until warmed through. Meanwhile, have your kids use 2 1/2- or 3-inch cookie cutters to cut the tortillas into pairs of matching shapes (ideally, you'll end up with 12 to 16 pairs).
Place one of each pair of shapes on your work surface and sprinkle cheese on them. Add a tablespoon of the chicken mixture and a little more cheese, then top with the matching tortilla shapes.
Right before serving, place the assembled tortillas, a few at a time, on a warmed griddle and cook over moderate heat for 2 minutes on each side. As you cook them, transfer the tortillas to a baking sheet kept in a warm oven until the whole batch is done. Serve at once. Makes 8 to 10 servings.