Hi there, and welcome to planDisney! I'm so glad that you've found us here with this great question about planning a Walt Disney World Resort vacation. It sounds like you're hoping to help your nieces and nephews have a magical experience! This is such a generous idea!
You should be able to purchase 
Florida Resident Disney Theme Park tickets for your nieces and nephews who are under the age of 18. When you purchase the tickets, you'll be given the option to 
verify your residency online using valid 
identification. If you're unable to do this online ahead of time, you'll need to accompany your family to Walt Disney World Resort to activate the tickets before they're able to be used. 
While you're on the Walt Disney World Resort website, be sure to check out the 
Special Offers page and see if anything applies to you as a Florida Resident. You never know what might inspire you to plan a vacation of your own!
I hope this is helpful to you as you assist your family in planning an incredible vacation to the Most Magical Place on Earth! Please stop back by 
planDisney with any other questions you have as you continue in the planning process.
Have a magical day!
Jennifer