I would also second the recommendation to take a cab (although, I'm not sure about whether all taxis have car seats). It'll be much faster than having to deal with a transfer. The general rule of thumb is to allow 45 minutes per leg of the trip, so with a transfer, that would be upwards of 1.5 hours (this is just in case you just miss the bus and have to wait for the next one). The taxi can get you there in less than 20 minutes (it'll be about $25 plus tip). I don't have experience with Uber at WDW, but I know that there are almost always taxis waiting in the taxi stand at the Boardwalk. Just head out the main entrance and you'll see them to your left (otherwise, one of the valet folks can help you flag one down).