Hi Melanie!
Character Greeting experiences can be a magical highlight to any family's Walt Disney World vacation.
The Disney website offers a multitude of
Character Meet and Greet locations but even more exciting is the new My Disney Experience APP offered on smartphones to provide guests the character locations from the palm of their hand. If I check right now, I'd find dozens of Disney Characters to choose from at specified locations in each Theme Park today. Simply download the My Disney Experience APP and you'll see a prompt for "Explore By Activity" and "Characters."
A budget friendly tip I can suggest is to purchase an autograph book and Sharpie marker in advance. Your local dollar store, Target or Walmart will likely have several small books to choose from, often in Disney theme! I usually attach the marker to the book with string or something similar, preventing the dreaded, "Where's the pen!" moment upon a surprise interaction with our favorites.
Perhaps your nieces would enjoy collecting autographs on a photo mat? We've done this in the past with our son and daughter and they've framed their favorite trip photo adorned with the Disney Character's autographs.
You might also check out
Character Dining Experiences, allowing your family unique, personal interactions with Characters while you dine. With their popularity, Advanced Dining Reservations are a must.
I wish you a MAGICAL vacation, Melanie, and please visit us again soon with additional questions!
Sherri