Please check out www.guineapigcages.com and do as much research as you can. Guinea pigs, bull especially, need LOTS of room or they will tear each other apart, or get mean. I have raised them, and have two currently in a C&C cage. There is so much to learn about cavies that isn't obvious.
That being said, do your children have a favorite book? We named ours Fern and Charlotte, after Charlotte's web.