Smaller African Cichlids... like Tanganyika and Victorians. They are hardy and will easily have babies which can do the whole circle of life lesson. They don't mind if you don't do much maintenance as long as they get fed... and water changes are easy.
Some of the Victorian Haps (obliqudens, for example) are as beautiful as they get and you can have a nice less about males needing to be colorful to attract female, and all of that stuff.
Some of these fish are 2-3 inches max.
I always recommend Africans to people who want saltwater fish since they can be just as beautiful with about 10% of the work and knowledge.