I think gold fishes are still one of the best fishes for children. Aside from being inexpensive, these fishes are readily available almost anywhere. However, if you're looking for some fancy fishes, you might want to try the fluorescent fishes, which are now being referred to as Glofish. These fishes come in different colors such as Electric Green, Moonrise Pink, and Cosmic Blue.
These fluorescent fishes are the first publicly genetically engineered pets. Essentially, they are the common zebra fishes that thrive in Bangladesh. Scientists then, through various researches, were able to come up with the idea of extracting the protein from jellyfishes and inserting them into the zebra fish genome, which in turn makes them fluoresce under blue light.