I've gone to the Flyers Carnival for three years now, this year will be my fourth.
If you purchased tickets for certain guys (The Flyers allow 2 auto or photo tickets per admission ticket) These guys are the top guys on the team, at least the most wanted. This year me and my dad are going and I have pictures with Forsberg and Gagne and auto's with Forsberg and Knuble. I'd suggest if you have a ticket like this, you try to get in line as early as you can so you get through the line quick and can move onto other things you want to get. If you decide to wait, the lines get extremely long. The players are scheduled for certain times, as many players do photos as well as autos.
For stuff you should bring, I'd bring any high end memorbilia that you want signed because almost all players give quality autographs at these events. I'd also be just as organized as you are when you normally get autographs because if you want many players you need to have your stuff together.
Also look out for an alumni table because the Flyers have this as well and maybe Boston will have Bourque and/or Neely at their event.
These may be obvious suggestions, but I figured I'd give them anyway.
PS - For your 10 year old, the Flyers have a portion of the ice open during their event where you get two shots on either Esche or another goalie for I believe 10 dollars... possibly the Bruins would do this as well.