Hi, Tina!
Welcome to the Disney Parks Moms Panel! I have visited Walt Disney World resort with my two kids on my own, and I want to ease your concerns!
Some attractions have space for only two people at a time, but often that third person will have the opportunity to sit in a row near you with another single rider or someone else who is in a group of three or five (or more). If you're worried specifically about
Disney's Haunted Mansion, you will be able to fit an adult and two kids on the attraction with no problem.
If you're curious, Disney created this
great planning resource for traveling to Disney World with preschoolers and young kids. There's so much fun for all ages, even a mom, and her two great kids.
I'm happy to
answer any extra questions you have before your unforgettable visit to Walt Disney World Resort!
-Jen