A magid shouldnt have a problem finding stuff to say that will keep kids awake. We do what many others have said ie make the seder on their level, involve them and make a small spiel. This is what they will remember for years to come. Giving them coke is a nice idea.
But definitely the best, proven, certain, guaranteed, true tried and tested method of being sure your kids stay up and stay alert at any time is… To try sending them to bed!!