Hi Kevin,
Thank you so much for visiting the Disney Parks Moms Panel with your question.
I think that whether your plan is realistic really depends on your unique family. You know your children best, and know how much stamina they have. There will be a lot of walking in your plan, so if they tire easily, they might get grouchy. If you have a very energetic family, this might not be a problem at all.
I suggest that if you do decide to go with this plan, that you narrow down which attractions you would like to experience, especially at Disney's Animal Kingdom, Epcot, and Disney's Hollywood Studios. Since you will only have a half a day at each, I think that as a family you should decide on no more that three attractions total that you would like to experience at each park. By doing this, you set the expectation that getting those three attractions in is great, and anything above and beyond this is a bonus. If you have not done so yet, order the
Walt Disney World planning DVD. It is free of charge, and you can watch it together and decide which attractions appeal to you.
I really like the idea of going in with a plan, but then being flexible enough to change the plan if you need to. If you are at Disney's Animal Kingdom and find that you absolutely love the park and do not want to leave, I would stay! Also, maybe one of your days at Magic Kingdom Park you will decide that you are tired and want to go back to your resort and rest and swim.
I hope that these thoughts are helpful for you, Kevin! Have a great time planning your vacation, and please do not hesitate to ask if you have any further questions.