The basic rules to Tag are quite simple. All you need is a group of kids and a decent sized backyard. One person is designated as "it", and that person runs around and tries to touch someone else. If they succeed, the person they touch is now "it" and tries to chase everyone else. The game continues until everyone is exhausted or until Mom finishes that batch of chocolate chip cookies!
This is another game with many variations. Here are a few:
Jungle Gym Tag
Tiggy Off Ground Tag
Toilet or Turtle Tag