It was an old story, maybe in the 70's, and it had aliens land, and some kids found them and kept them as pets, they were very small, obviously, but eventually their parents told them they had to let them go.
The kicker of the story was the last scene, where the kids and their parents were standing watching the aliens take off in their spaceship, and because of the description you suddenly realize that the kids and their parents were non-humans, and the 'aliens' were humans.
This bears some similarities to "Youth", a short story by Isaac Asimov. First published in 1952, it is certainly an old story - much older than the 1970s. It deals with some aliens seeking a trade deal with a new planet, but things quickly get out of hand after they crash and are found by the children of the locals they were supposed to meet. The children are named as "Red" and "Slim" and behave generally as perfectly ordinary human children. They indeed keep the unusual bipedal animals they find as pets, and plan to make big money by exhibiting them at the circus. The twist comes at the end when:
Red watched the ship leave. His red tentacles, which gave him his nickname, quivered their regret at lost opportunity to the very last, and the eyes at their tips filled with drifting yellowish crystals that were the equivalent of Earthly tears.
It is available at Project Gutenberg if you want to check.
