Hi Sarah, Welcome to the Disney Parks Moms Panel! I hope that you're dreaming of sunnier days right now and are very much looking forward to your Walt Disney World Resort vacation!
The average temp in April is around 80 (F), and sunny days (or really humid ones) can make it feel so much hotter. I was in Orlando in March of last year and the weather was perfect, but I felt like swimming with my son in our Resort Hotel's kiddie pool was a bit cold. I was also at Disney World in May of 2015 and almost melted. So I personally think that 80 degree (F) April weather sounds just right for some splashin' fun at both
Walt Disney World Resort Water Parks,
Typhoon Lagoon and
Disney's Blizzard Beach.
Also note that just in case that some weird cool streak happens, or the skies are cloudy, the majority of Walt Disney World Resort pools are heated to a very comfortable 80 degrees (F). This includes the various pools and slides at both water parks. I personally have found a kiddie pool or two at a few resort hotels that were not heated at the time of my visit, but as far as a full day at the Water Parks you should be good to go.
I hope this helped in your trip planning, Sarah, and we'll see you real soon!
~Kristen