I think taking your child for any birthday will be magical and memorable! I am a mother to two children (DD5 & DD2), and my DH and I have toured WDW when the youngest was only 8 mos. old. You've probably been to WDW before sans kids. Now you get to view WDW thru the eyes of your child, which will probably lead to new and picture worthy experiences (some good and some not so good).
Echoing the previous posters, if you're prepared to take your time, have a place to nap (my DD's always snooze in the stroller), keep meal times somewhat regular, a cup and snack handy, a camera "on-the-ready," and concede to the fact that you might not get EVERYTHING at WDW in during this trip, you'll be just fine and a much savvier traveler! BONUS: Your child is FREE until 3 y.o.!
I find with my youngest that she liked the parades, especially the afternoon one at MK, where she could actually interact with the dancers and characters! We only schedule one sit-down meal (typically a character buffet) because DD2 cannot stay still for more than 10 minutes, which makes quick-service meals ideal. Also, we hit up each park at or shortly after opening, head straight for the most popular rides (especially at MK in Fantasyland). Then we slow things down a bit with a parade, stage show, face painting, character meet-and-greets, or finding a not-so-crowded spot in the parks to let our children "escape" the stroller and walk. Typically, we'd head back to our hotel late-afternoon, where they could safely burn-off some pent up energy (i.e. swimming, exploring the grounds, running around the hotel room while DH and I actually got to sit for more than 5 minutes). After a 2-hour park break, we'd head back out to another park, but would go at a much leisurely pace. We'd hit up any rides with a short wait time, watch the nighttime parade or fireworks display, and call it a night by 8-9 p.m.
Any trip with a toddler in tow is an adventure, so enjoy the ride! :wave: