K.H.
I just got back from Disney World with my two girls (almost 5 and 20 months). As others have mentioned, you will need a stroller (for both kids) due to the amount of walking. You can either bring your own stroller (double or two umbrella) or rent one. I used Orlando Stroller Rentals (http://www.orlandostrollerrentals.com/) b/c it was cheaper than renting a Disney stroller and I had the stroller even when we weren't in the parks. I didn't have a double stroller to bring, and I loved the one they provided! The MOMS panel off of the Disney web site has information on everything... you can pretty much search anything you have a question on.
One of the biggest pieces of advice I can give is to pace yourself. Know what your kids can/cannot handle and work around that. You don't want to have cranky kids and cranky parents b/c you decide to do too much. A lot of families recommend leaving the park in the afternoon for naps/swimming etc and then returning in the evenings. My girls actually did better getting to the parks at open and staying until mid afternoon or so. We then ate dinner and were able to relax in the evenings and get to bed early. I would recommend going to the Magic Kingdom night parade and fireworks.
I'm not sure which parks you are planning on going to. My daughter actually really liked EPCOT - Spaceship Earth, Nemo ride, Turtle Talk with Crush etc. When you go to Magic Kingom, go to the Dumbo ride first thing (if your boys are into it). The line gets crazy long very early in the day. We were able to do most of the rides in that area with little to no wait. FYI - the Snow White ride is mostly in the dark (some kids get afraid) and the Lilo & Stitch ride usually isn't recommended for young kids due to the scare factor. Buzz Light Year ride is lots of fun!
If your kids are into character greetings, check out the maps of where you are likely to find characters during the day. You might also want to do a character breakfast so your kids are guaranteed to see a few characters at once.
Hope you have a great trip!