Welcome to planDisney, Nina!
I'm so happy to be chatting with you today, and hope that I can give you a little guidance in regard to your question! My husband and I enjoy going to the theme parks solo for a meal or a few rides, sometimes! Since we're local, we use babysitters in our area that we trust to watch our kids while we are out. I have heard that there are some reputable third-party babysitting services near Disney World for people staying at Disney Resort Hotels that you may want to look into -- just please do extensive research before choosing a service to be sure that it is trustworthy.
Disney used to have a wider variety of child-watch a few years ago, but at the time of writing this, there is only one to my knowledge.
Camp Dolphin is a children's activity center that was designed to help parents have a child-free night while the kids enjoy a dinner, games, crafts, and more! This camp is specifically for 5–12-year-olds and operates from 4pm-11pm at the Walt Disney World Dolphin Hotel. Pricing, reservations, and additional information can be obtained by calling Camp Dolphin directly. (Advance reservations are required for this.)
I hope that you and your fiancé are able to have an enjoyable, child-free, time at Disney World, but if you're not able to find the childcare you need, I recommend checking out
Garden Grill at EPCOT for a quiet mealtime. This slowly rotating restaurant gives a good amount of privacy, and has characters coming around to engage with the kids! It's a fun time for the whole family.
If you have any additional questions, we'd love to hear from you again and hope that we can help you further!
See ya real soon,
Allyn