I'm torn on this. I definitely agree with safety being an issue in this day and age, but I also think it may be a little over the top to have an 8 year old glued to a parent's side the entire time in a book store.

If I was the store employee (pretending there is no policy), I would have kept an eye on your son but left him alone unless he was being disruptive/stealing/etc. I wouldn't have said anything, especially not after a measly 5 minutes.
Now if a half hour later he was still by himself, I would start wondering where the parent(s) were and start looking around for you.

It is probably much easier for the company to just stick to a "all children must stay with parents" policy and I understand where B&N is coming from. But still, if your son is anything like me, I like to take my time picking out a book without anyone trailing me around a store, whether it's an employee, parent, or friend.

So, I'm still not sure where to stand on this, since I agree with both sides.