Hi, Shelley!
So glad you're back with another question!
To be honest, we've been in Walt Disney World in early January when it had dipped down to 36 degrees (we though the pilot was joking when he sold us the temp as we made our decent to land...he wasn't!) and we've been there when it was 70 degrees. (One year, it was freezing when we landed, then warm enough to swim five days later.)
Because the resort pools are heated beautifully, we always bring bathing suits because it can be warm enough to swim even when you didn't expect it. Keep in mind, too, that all of the Disney Vacation Club Resorts have their own Community Hall. We've used these great locations on pool days during the cooler months. If it's warm enough to swim for a little while, but not an entire day, we head to Community Hall for crafts, games, video rentals (free to DVC Members) and even hands-on activities that your little princes can enjoy.
If you decide that it's not warm enough to swim and are looking to head someplace other than a park, consider some time at
Downtown Disney. Between World of Disney (the world's largest Disney Store), Once Upon a Toy, AMC Downtown Disney 24 (movie time!), the soon-to-open Splitsville Luxury Lanes (bowling!) and lots of kid-friendly dining options, you could easily spend quite a few hours having fun in this non-ticketed venue.
Enjoy your planning! Be sure to send more questions as you think of them, Shelley; we love to help!