Howdy Kayla! What a fun way to celebrate your daughter's 2nd birthday!
My first suggestion is to make sure you get a celebration button for her. They have generic "I'm Celebrating!" buttons too so be creative and come up with something fun that your 5 year old is celebrating as well. The birthday buttons are a sign to Cast Members and you never know when they might add some magic to her day!
Disney has created a number of ways for you to celebrate
special occasions. Be sure to check them out and see if any would be a good fit for your trip.
As far as coping with the crowds, the fact that you are preparing for them is half the battle. It will be crowded but remember that you are at Disney World and try to enjoy each moment. We typically try to get to the theme parks early and enjoy the cooler mornings with lower crowd levels. Later, we usually head back to our resort and enjoy the swimming pool or nap time. There are some great places to just sit and take a break during the day and I encourage you not to push yourself. Make a list of the must do attractions. Try to experience those first and then consider anything else as a bonus.
Are you taking a stroller? If so, take a blanket or towel that you can place on the stroller to keep it covered when you are not using it. The stroller will get hot in the sun and burn sensitive skin.
Be sure to check out the Baby Care Centers located in each of the 4 theme parks. They are fully staffed and provide a convenient place to feed, change and nurse little ones. They also have a tv, books and a few toys that your 5 year old can enjoy while you tend to your 2 year old.
I'm so excited for you and know you are going to have a magical vacation. Please let me know if you have any other questions.