Hi Traci!
Thank you for sending in your question to the Moms Panel! Some panelists recently answered a question about a first trip to Walt Disney World. You can see the various viewpoints
here.
My children, ages 5 and 10, love the water parks. They prefer Typhoon Lagoon over Blizzard Beach, but I think you can easily find children and panelists who would say just the opposite. You really can't go wrong with either.
The water parks and the pools at Walt Disney World are heated, so it is possible to swim all year round. However, when it gets unseasonably cold (such as the rare occurrence of snow at Walt Disney World), Disney will close the water parks. Also the water parks close during the winter for refurbishment, but not at the same time -- one is always available for guests.
With regards to the food allergies, definitely mention it when you make dining reservations. Also, when you arrive at the restaurant, tell the Cast Member again. Disney does a great job handling food allergy issues. I've seen the chef come out many times and talk to guests about what can be special made, eaten, etc.
Enjoy planning and write back if you have any more questions!