Hi Scott,
Have you considered an, "In Room Celebration"? These special surprises are arranged while your family is out enjoying the Parks. You come back to your room to find that Mickey and his friends have left some gifts for you. See
HERE for more information. If you were thinking of something a little less expensive, there are other fun ideas on that site as well. If you did the In Room Celebration on your first night, some of the packages leave a light up Tink in the room somewhere part of the surprise. You could really play that up each night by continuing to leave surprises yourself. One night you may want to leave some
Disney Gift Cards so the kids can pick out their own souvenirs (just be sure to keep them in your wallet as they are the same as cash).
One simple little thing that I've done in the past, which my kids still remember, is I wrote out a rhyming riddle for each day. Then I tucked it in an envelope with the day of the week written on front and sealed it with a fun Disney sticker. In the morning the kids got to open it and try to figure out which Park we were headed to for the day. Your children may be a bit young for this, but I think your 5 year old would find it fun if you made it as simple as drawing a sketch of Cinderella Castle, Spaceship Earth (Epcot), Mickey's Hat (Hollywood Studio) and the Tree of Life (Animal Kingdom). Then have the kids look for this big icon when they get to the Parks (it's impossible to miss them).
Have a wonderful vacation with your family,
Kaylene