apguns,
I agree with the others that there are usually too many variables at the time to say what anyone would have done in your place. However, I would suggest that you do tell police and store security now, even if it is after-the-fact and let them do what they can to identify the perpetrator from the tapes. Different stores keep them for different lengths of time and they might still be able to identify him.
Second, Your oldest child is old enough to be part of your family security. Explain your security to him. Take him shooting with you and let him understand and enjoy shooting with you. Explain guns are fun and dangerous and only handled with you. Show him how to unload them and how to make them safe. These are things that take away the "Forbidden Fruit" syndrome that cause kids to look for guns and want to "play" with them. The more they associate with them, the less "special" they are. Also tell him to scream his head off the next time a stranger tries to touch him or his brother in a store and to not stop until you or a security officer arrives AND that he will not be in trouble for it no matter what. It's amazing how many children won't make a scene because they are afraid they will be punished if they do. The next time your youngest gets touched, your oldest should turn into an air raid siren! Make sure to go outside and practice it with him - kids love to scream! And make sure they understand it's for emergencies only. Kids should always be a part of the family's emergency plans.