As a standard negotiating tactic, I would not tell them any numbers. Let them make an offer if they are interested. You tell them a number, and I can guarantee their offer will be a "little" bit more or equivalent to your present offer. You let them make the offer, and it could be much more than the previous offer. If they offer less, you can then reveal your offer if you think it is necessary to get them to budge. Be mindful that they may not be able to budge based on their present budget. If it is someplace your son is dying to attend, try not to kill the golden goose over pride and money - unless money is a paramount issue to your family.
Certainly OK to let them know you have an offer on the table however in "their" conference.