I think you are doing a great job helping your children make good food choices. There are plenty of things that will work, and as you have found what is good for one swimmer is not as good for another. Some of the choices will vary based on timing - what works if eaten three or more hours prior to a meet might be a bad choice eaten 30-minutes prior to a meet!
The meal decision requires some real-world testing, and with a day or two to go before the meet it may be a bit too late to try new things. I suggest you go with what you know works for each of them, regardless of whether it is a breakfast, lunch, or dinner type of meal. What is their favorite pre-swim meal? Go with it! It could be pasta, noodles, rice, cereal, toast, eggs, a sub-type sandwich, pancakes, waffles, even a peanut butter sandwich - as long as it is a meal that hits the main food groups, is easy for them to digest, and is familiar to them.
Get that main meal done two to three hours prior to swimming, then "keep the fuel tank topped off" with easy to digest, lighter foods - fruit (apples, oranges, bananas, raisins, pears, etc.), power bars, sport drink, pretzels, pop-tarts, a simple sandwich (peanut putter and banana, banana and honey, jam, etc.), low-fat pudding, rice cakes, plain toast, etc.
Feed 'em what you know is good for them and what they think of as tasting good and that they feel good eating. Later on, try a few different things prior to swim practices and learn what other choices may work for your swimmers.
Swim On!
