Hi Victoria,
Happy Birthday!! I can't think of a better way to celebrate than by heading to the Magic Kingdom for the day!
While there are some attractions that have height requirements (click
HERE for a listing), you'll find that there are many attractions your entire family can enjoy together. Yes, the 3-D movie known as Mickey's PhilharMagic is definitely something you will all be able to experience.
If you want to experience an attraction that your children are to small to ride, Disney has a rider switch program in place. It's absolutely FREE. At the entrance to the attraction, ask for a rider switch pass. You can stand in line to ride while the other adult in your party watches the children. They don't have to hang around and wait for you - maybe they could grab a snack or play at Pooh's Thoughtful Spot. Later, the second adult takes the pass to the attraction and will be admitted with very little wait time.
Hope this helps. Have a magical vacation!