Having done this with two young children, I know how important it is to get out quickly at the end of the fireworks. The kids have had it, and to wait around for another hour as the crowds leave often won't cut it for the little ones. About an hour and a half (yes, that long) before the fireworks, make your way toward the exit and find a spot by the train station at the end of Main Street. Someone can sit and "hold" the spot while another person takes the kids into the shops, for a round the park train ride, or for ice cream. Make sure to get back to your spot about a half hour before the fireworks, because it gets crowded! Once the last firework ends, make a bee line out of the park and for your transportation. The monorail, bus and boat lines build very quickly. However, by being toward the front of the pack leaving, you have a definite advantage of being among the first groups to board.
Good luck!