First of all, make sure that cameras really aren't allowed. If they aren't, I don't recommended it. If you do get caught, you could ruin your son's birthday by getting thrown out of the concert. Is a few pictures of something both of you are likely to remember very fondly anyway really worth it?
On the other hand, just think how cool it will be for both of you to tell how you got thrown out of a rock concert with you dad/son.