Hi, Amanda! Thanks for the question. How awesome that your son's first visit will be his birthday too! The Contemporary is an awesome resort, especially with little ones. The monorail is so handy for visiting the Magic Kingdom and Epcot - especially if he falls asleep in the stroller. If that's the case, you can let him keep sleeping without having to unload him.
It's also easy to visit some of the great restaurants on the monorail loop. 1900 Park Fare at the Grand Floridian or Chef Mickey's at the Contemporary would be great places for his birthday meal. For you and dad, make sure to get a cup of Kona coffee at the Poly. Most coffee elsewhere is, er, awful.
Now that we've talked food and transportation, let's talk about the parks. The
Traveling with Little Ones page on the Disney World website includes a link on the right hand side for attraction height requirements. Many attractions have no height requirement at all. In fact, nothing in Fantasyland in the Magic Kingdom has a height requirement. Start with more easy-going rides to help your son become acclimated to the type of experience he can expect from attractions.
For example, there are several attractions that use boats to move guests through the experience. He'll feel much more prepared for Pirates of the Caribbean or Maelstrom, for example, if you take him on it's a small world, Living with the Land or Gran Fiesta Tour first. Taking similar precautions can also help with other experiences. For dark rides, start with Peter Pan's Flight or The Many Adventures of Winnie the Pooh before considering Snow White's Scary Adventures or the Haunted Mansion.
Check out TouringPlans.com crowd calendar for tips on which parks to visit each day, and come on back if you have any other questions!