Hello Andre and thanks for bringing your question to the Disney Parks Moms Panel.
Disney's Dolphins in Depth at Epcot is both a wonderful and very insightful program and because
shorty style wet suits are provided for Guests it's suitable at most times of the year; that being said, the Florida sunshine is of course much warmer in May than it is in February!
I'm sure you'll already know this, but dolphins and all the sea creatures are kept in near-as-natural an environment as possible at
The Seas with Nemo & Friends; the sea water in the 5.7 million gallon aquarium is not heated meaning that even in the hot summer months the water temperature is very likely to feel somewhat chilly to us humans!
Just so you know,
Disney's Dolphins in Depth is not a swim with dolphins rather a guided tour with an expert trainer which includes a 30 minute waist deep in water interaction with the dolphins.
You may also be interested in the snorkel experience -
Epcot Seas Aqua Tour or for SCUBA-certified Guests the
Epcot DiveQuest program.
I'm sure which ever activity is decided upon you'll enjoy a magical time making memories at Walt Disney World Resort which are sure to last an entire lifetime.
Have a great Disney day.
~ Jane