J.G.
Ok, I'm a Disney fanatic, so bear with me!
We took our son when he was 2 years and 3 months. We planned on doing a park in the morning, going to the resort for taking a nap and going to another park in the evening. We were going to take everything easy and not push too hard. Well, he NEVER wound down. Going to the resort in the middle of the day was horrible, he was too wound up to rest. We ended up staying at the park and closed most of them down at night! Even then he was still awake on the bus back! We all had a great time! We only hit 1 park for early magic hours (which avoiding is a hit or miss on crowd level, so we usually take advantage of them) and slept in a little. We rode the things we wanted and "child swapped" for what we wanted that he couldn't do.
I say go for it! If you would like more information and trip reports from a lot of people, especially with kids, try www.mousebuzz.com. We are Disney fanatics, but you can get a lot of useful information.
If I can help at all with planning, just e-mail me. I like to do it as a hobby (yes, I'm possessed) and usually have trips "planned", even though we're not going anytime soon!
We've also been to Disneyland (last May, our son was almost 3) and I just love Walt Disney World more. It was special to see the place where it all began, but love the variety at WDW. Magic Kingdoms at both are similar, but not exact duplicates. Yes, there are only 2 parks, but we didn't find as much to do for our little one at DL.