Welcome to the Disney Parks Moms Panel! Happy first visit and hooray for birthday celebrations!
Definitely consider making dining reservations for the special day(s) and enjoy one of the yummy Cakes at Walt Disney World Resort. Be sure to make a note of their birthdays on your dining reservations so that the girls can get a little extra special treatment at the restaurants!
We love to celebrate my husband's birthday at California Grill by making a dining reservation during the Happily Ever After fireworks. Given your girls ages, they might prefer 'Ohana. If you make a reservation for about 30 minutes prior to the fireworks show (just check the times for the dates of your visit), arrive 20-30 minutes early to check-in and request a window table. We had a perfect view of Cinderella Castle on our last visit and the show's music was piped into the restaurant. Of course, if you want to be in the midst of the magic for the Happily Ever After show, stake out a viewing spot at least an hour and a half prior to the show. You could also do a pre-park opening breakfast reservation at Akershus Royal Banquet Hall. If you finish dining around 9:00 a.m., you can jump in the stand-by line for Frozen Ever After and use one of your Fast Pass+ selections for another attraction.
Marcy, also make Fast Pass+ selections for their favorite attractions. Definitely check the height requirements prior to making those Fast Pass+ selections. I hope your little one is tall enough to ride Avatar Flight of Passage. It is a must do-experience on your expedition to Pandora - The World of Avatar. If not, be sure to use a Fast Pass+ for Na'vi River Journey. Kilimanjaro Safaris, Expedition Everest - Legend of the Forbidden Mountain and The Festival of the Lion King are also favorites of ours at Disney's Animal Kingdom!