All these replies and the message still has not gotten through. You may know everything there is to know about your son. That has nothing whatsoever to do with the other people in the store. Some psycho could grab your kid and be gone in the time it takes to say "Where's Timmy?".
It does not matter if your child is Doogie Howser, Stephen Hawkings and Einstein reincarnate, YOU DO NOT LEAVE YOUR CHILD ALONE, OUT OF SIGHT AT ANY STORE FOR ANY REASON. It does not matter if he spends $100.00 a day, everyday of every week. He can be the best customer they have. He is still a child and potential target.