There are countless opportunities to meet with characters throughout Disney's parks. You'll want to do some research about who will be where and when, and perhaps use a FastPass+ or two to ensure time with your family's favourites (you can use them at Princess Fairytale Hall in Magic Kingdom and Mickey's Character Spot in Epcot). Even better, book character meals where you're guaranteed to encounter at least one (often several) and have a more personal experience. You can hang with Mickey and crew at Chef Mickey's, partake in a royal meet-and-greet at Disney's Perfectly Princess Tea party, or have a Polynesian experience with Lilo, Stitch, and more at 'Ohana, to name a few.
Bonus tip: Book some of Disney's festive and other special events for access to even more characters (Moana was one of the hidden gems at the latest Mickey's Not-So-Scary Halloween Party), and be sure to catch the parade featuring many more Disney faves.