Hello Andrea! Thats a great question. As of right now when you purchase a vacation package including a stay at a Walt Disney World Resort Hotel, you get a set of complimentary MagicBands. These MagicBands are the solid color bands that you are talking about in your question. The special
retail MagicBands with the characters on them are available for purchase on the Disney Store website or on Walt Disney World Property. There is currently no way to order them in lieu of the solid color MagicBands. The good thing about the retail MagicBand is that after you link it to your account you can use it over and over and opt to not receive the complimentary solid color MagicBands. This way you can get your money's worth in purchasing the special retail MagicBands.
If you'd rather go for the complimentary solid color MagicBands there are many ways to decorate them. I love the MagicBandits sets, and they are cheaper than buying the character MagicBands. I have the gem set and they definitely add that extra touch to the solid color bands. There is a Frozen set that has Anna, Olaf, a snowflake, and Elsa that your children might like. These are also available for purchase on the Disney Store website or in the parks.
If you have any more questions, please let us know and we'd be happy to help. Have a magical Walt Disney World vacation!