Many people will disagree with me. We DO pull our children out of school to go to WDW. While school is very important and we wholeheartedly support our children in all things school, there is more to the life of a family and their children than school. We will not be on this earth forever and your children will only be this age only once. If April works for you, I'd say go for it! Making family memories and gaining some real world experience (airports, traveling, new experiences, new scenery, people, handling being in a different place) is just as important as school learning.
I suppose we could go in the summer and accomplish the same thing, but we tried that once for our first trip ever to WDW. The crowds and heat took away a lot of the magic for us, especially DH who we found out does not do well in heat. The kids had meltdowns because we were so hot even though we took breaks and went back to the hotel for the afternoons and left the parks early for night. This does not make for good family memories. We now usually go in April and it's just right for us. The parks aren't open as late, but they are less crowded so you can accomplish more in any given day than the summer. It's still warm enough to go back to your hotel to swim and take breaks from the parks. Do what you think is best for your family and don't feel guilty about it!