Hi Dana,
Epcot and Disney's Hollywood Studios are my two favorite parks, so this question just makes my day! While my two kids, age 3 and 8, love to visit both parks, I would say that
Hollywood Studios will give you a full day of family adventure that everyone can enjoy.
There are great family-friendly attractions like Toy Story Midway Mania, Voyage of the Little Mermaid, The Great Movie Ride and Muppet*Vision 3-D. The kids can run off some steam at Honey, I Shrunk the Kids Movie Set Adventure and Jedi Academy, after having lunch at 50's Prime Time Cafe or Hollywood and Vine. Also make sure to check out some of the live shows, like Lights, Motors, Action -- Extreme Stunt Show, Beauty and the Beast -- Live on Stage, and the best show ever,
Fantasmic!
I hope this answered your question. If you have any more questions before your vacation, Dana, feel free to ask us at any time.
Have a fantastical Disney day!