I love Disney; growing up, I visited Disneyland more times than one can count, and I have been to WDW several times since it first opened. My purpose is to give a heads up on the crowds that pack into WDW. With some research, plan your trip when crowds are not so bad if at all possible. In addition, this last trip we took was a first with a toddler in tow, and it was a challenge. First, we visited the week BEFORE Thanksgiving--by all accounts a less busy time. WRONG. The parks were so packed with people, it was difficult just walking, and every ride had huge lines and made the day stressful. We weren't the only families that thought it was overcrowded, and many said they were not having fun.
But the Disney parks are far superior in detail and decoration (anytime of year). We did get to enjoy the parks decked out for Christmas, and my two younger children were in awe most of the time. Weather can get cold in Orlando--some nights were in the 30s on our visit, and some days were only 50ish. Be prepared to bring hats and gloves for the kids and avoid the water rides in cooler temps. Be aware that anytime near a holiday is busy in all the Orlando theme parks. Employees told me a great time to visit is in October just before Halloween. The crowds on this last trip were the worst I had ever seen, even in summer.
TIPS: Use Fast Pass--it is only good for one ride at a time, so choose the most popular ride. Some kids bring a stroller that folds quickly and easily. That way, you can get it on the trams, monorail, MK Train fast. I prefer to bring my own if we are driving, but if you rent a stroller, tie something on it to quickly pick it out from the sea of strollers (plus, it is less likely to be taken if you tie stuff on it).
You will NOT be able to see and do it all with little ones in tow, so pace yourself and try to enjoy yourself regardless of how much you get to ride, etc. Younger kids don't get to ride or do very much, but they do like to watch and see everything. Dine at one of the many restuarants, Disney's food is much better than other theme parks and the break is needed! DO bring a couple of juice boxes and a bottle of water, in a tote or backpack. If staying at a Disney resort, USE the package service that! Go online to get the event schedules for parades and shows to better than your day. Go early, leave in the afternoon for a room break, so back in the evening especially with younger kids. My kids love the monorail, ask if you can ride with the driver!