Staying at the hotel would be great if you can swing it. I know my DD10 would love it if we stayed on property. If your kids are like mine is (and my siblings and I were) they will want to go swimming, even if it's cold.
Maybe you could do a special meal-Goofy's Kitchen? I know as AP holders we haven't done any of the character meals at DLR, only at WDW so it would be special if we did one at DL.
Oh, and if you do stay at the hotel you could have a special gift basket delivered to the room for him. I would put it together myself and then figure out a way to get it to the front desk so they could deliver it for me. Or as you're leaving the room to go to the parks on his bday, "remember" you left something in the room and go back for it. Then bring out the gifts and leave them in the room for him to discover when he gets back. I did something similar for my DD a few years back at WDW. My DM took her to the pool (I didn't want to go) and while they were gone I decorated the room and brought out the presents. She was very happy when she got back to the room.
I think you can also have Disney deliver something to the room-I like doing it myself (it also saves some $$)
Have a great time!
