Welcome to the forum. If you mean Necturus maculosus
as a mudpuppy, I have plenty of pictures. The term "mudpuppy" is applied to many salamander species. I dont know if you were looking for real pictures or drawings. What is this children's book? Are your writing one? Will this be a published book? If it is and you'd decide to use any pictures, you would need my permission for there use. This would go for anyone who offers you pictures/drawings.
This is a picture of mine: Cool Mudpuppy Shot
These (except the first) are a little old.