Amphibians

Amphibians lay their eggs in water, and young amphibians tend to resemble small fish.

The tadpole, or newborn frog, is born and lives in water. It has a tail that allows it to swim like a fish. It also has gills so that it can breathe under water. As the tadpole grow into a frog, it loses its gills and tail, and develops legs for moving on land. Most amphibians can both walk and swim in water.

source:
http://www.kidport.com /RefLib/Science/Animals/Amphibians.htm