You can request to be on a waitlist for main dining and it may or may not come through. If you do have late dining, there are plenty of snack options for staving off the hunger of starving family members. Depending on the ages of your children, they may want to have dinner with the Club/Lab in order to do some of the other activities that are scheduled during the late dinner time. You can order something from room service, grab something from Goofy's Galley, Pinocchio's Pizza, or Pluto's, or, even better, stop by Diversions or the Promenade Lounge for some pre-dinner snacks (like chips and salsa every night at the Promenade Lounge - they start at 5 p.m. so it won't be too close to dinner to spoil an appetite).