Tadpoles are the larval stage of development for many amphibians. While other amphibians have larval stages, many people associate tadpoles as being baby frogs. Frog tadpoles start out with no legs, breathing through gills and moving with a tail. They develop into adult frogs over time, growing legs and eventually losing their tail and gills. Tadpoles present a number of options for costumes for infants and adults.
An infant tadpole costume presents a good fit in terms of executable qualities and metaphorically since a tadpole is the immature stage of a frog. The youngest tadpoles are more like fish than frogs, with no legs. That means a green sleeper with some eyes added to it would work as the costume. Of course, adding some frog legs and feet to the same sleeper brings the tadpole into a later stage of its development.
A tadpole costume, or more accurately several tadpole costumes, works quite well for a group costume scenario. One idea would involve a group of tadpoles, with essentially identical costumes. For a group of siblings, though, all different ages, a different take might involve tadpoles and frogs at different points in development. The smallest child could get the immature tadpole with no legs and a tail. An older child could have the same costume with the addition of feet and the transformation could go all the way up to full-frog costumes.
Teen or Adult Costume
For a teen or adult tadpole costume, a full one-piece costume could be an option, but might need to be sewn. Just use green cloth to create a full costume with a tail. Frog feet could be represented by the hands and legs. Round eyes should be added to the head. Otherwise green clothing with a tail attached with pins or sewn on could do the job. Green makeup as close to the color of the fabric should be worn on all exposed skin.
More unusual costumes come from variations on a tadpole idea. Creating a blue costume and covering it with small tadpole props creates a tadpole pond costume. Another idea would be a metamorphosis costume. Start with a tadpole costume with just tail at the bottom and at the top a frog's head and front feet could be leaping out and to the side, basically off the shoulders. Another idea would be creating a tadpole character by using the green makeup and basic costume for a tadpole, but add construction worker, biker or other clothing to create a characterization.