You may not need it for the smaller parks, MGM for example, but I at least reccomend it for AK. For my DD3.5 we'll at least do that. When my DD13 was that age she did all right in the rest of the parks, but AK was where we had the issue (of course it was also opening day, CROWDS). We ended up carrying her through the whole park. Though Epcot is big, it is really hard to go through WS with it. We might use it through MK to since it isn't quite as tight. I think we'll rent just because we don't want to lug her bumbleride through the airport.