Welcome back Megan! I am so happy you returned to ask another question, I have three children who have been traveling to Disney Parks since they were very small infants, so I have lots of ideas for you. I don't know if your seven year old is a thrill seeker like my daughter, but if he is you will love some of these different options at Disney's Animal Kingdom, Magic Kingdom, and Epcot.
At Animal Kingdom, check out Expedition Everest, and Kali River Rapids. Both of these rides are my 8 year-olds favorites. Your whole family will love the songs, and vibrant colors of
Finding Nemo-The Musical. Be sure to take your whole family on a tour of the Harambe Wildlife Reserve on
Kilimanjaro Safaris. Your 18 month old will love gazing at the animals.
Magic Kingdom is home to many classic Disney rides and characters. Your son will love conquering Disney's Mountain ranges: Space Mountain, Splash Mountain, and Big Thunder Mountain Railroad. This park also houses the most attractions your whole family will be able to enjoy together. Your 18 month old will be able to ride any attraction that does not have a height restriction posted. Make sure to take a ride on Dumbo the Flying Elephant, soar to Neverland on Peter Pan's Flight, and hop through the Hundred Acre Woods in a honey pot on The Many Adventures of Winnie the Pooh.
Epcot is home to some great attractions and experiences. Your son will love Soarin' and Test Track. Be sure to check out Innoventions East and West for fun interactive games, and exhibits the whole family will love.
~Jen