Hello Laura. I think it is so fun you are going to surprise your children with a trip to Walt Disney World. There is no better gift.
While it is true that you can make reservations for most things 180 days in advance, I would still go forth with your trip. We often times plan last minute trips and I am always surprised with what we are able to book. With that being said, you may not be able to reserve everything you want to do but I think you will be surprised about what will open up.
My biggest advice to you is to be persistent. I have been known to call everyday to try to get a reservation at one of my favorite places. Around 45 days prior to your trip is a great time to call because payment is due in full then. Unfortunately, some people have to cancel their Walt Disney World trips and reservations seem to open up around that time. So keep on trying!
The Bibbidi Bobbidi Boutique has 2 locations so if you can be flexible where you want to have it done it may be easier to get a reservation. Cinderella's Royal Table, at the Magic Kingdom, is not the only place to dine with Cinderella. You can also meet her for dinner at
1900 Park Fare located at the Grand Floridian. This would be a great alternative if you could not get the reservation that you wanted.
I think you will have a great time on your trip to Walt Disney World. Try to be flexible and persistent. It will pay off!