to watch the most game possible, your younger kids are going to have to have something to do. Hand-held electronics can come in handy with this. Coloring books, word puzzles, or other similar things will help out.
Plan on some eating, that can distract them for a bit. With the 8-year old, if they have any interest, explain what's happening on the field.
The problem is that you are taking them to an event that, at those ages, they are not excited about.
The 4-year old will be tough though.
Good luck.