Hi Heather,
Welcome to the Moms Panel!
I'm assuming that you intend on using a park ticket on the first day, so I would suggest taking the Monorail over to Epcot. Taking the "highway in the sky" is exciting, it's an attraction in itself for the little ones. I know my son would ride it all day if we allowed! You could walk from the Polynesian to the Transportation and Ticket Center where you would board the Monorail to Epcot or you could board the Monorail at the Polynesian, and get off at the fourth stop and transfer on to the Epcot Monorail (this could take 30 minutes, so walking would be quicker).
Once at Epcot there are plenty of things to experience right at the front section of the park, Future World. My kids love
Spaceship Earth, Soarin',
Test Track and
The Seas with Nemo and Friends.
Now, if there would be an opportunity to use that park ticket another day during your visit, I would suggest skipping the theme park and taking a trip to
Downtown Disney. This is a fantastic and FREE way to kick off your visit. They have Lego Imagination Center, Once Upon a Toy store, Goofy's Candy Company and so much more!
I hope this was helpful, have a great trip!