L.M.
First, don't worry about a present.
Second, if you are just going to provide cake and punch you don't need to say anything on the invitation. It's assumed that you will provide that. Also, it would be fine if that's all you were going to provide....you wouldnt be considered cheap. Now, if you want to have snacks also then you will write at the bottom of the invitation above the rsvp "Light snacks provided" or if you're going to have a full lunch then you'll write "Lunch provided". But you really don't need to provide a lunch, nobody would expect it. That's kind of late for little ones to wait for lunch. have fun.