"After all, if you get to the food area, what stops you from going to the movie."
What stops you from going into a movie is that it would be a crime? I have done it at two different theaters. At one you just let them know what you are doing and they wave you in. I would imagine if you did not come back out, they would follow up. (Granted this might be extra work and a theater could decide to have a policy against it. I would also imagine they would not let a whole group of teenagers do it, but I think they can take a little risk to make a sale to a middle aged woman. Its a judgment call and they really are not risking anything (similar to the reasoning of not placing guards at the movie exits to make sure you don't slip into a second movie).
At the other theater, you actually sign an in and out form.
It doesn't hurt to ask. If their policy allows it they are probably willing to bet that she isn't going to boldly lie in order to introduce her child to a life of crime : ).
Michelle