Enemies from the Deep (Alien Encounters)

Summary

On the planet Terranu, two families have established a research base to look for extraterrestrial life. One day four young friends spot a watery tentacle slither out of the nearby river... and a pair of eyes watching from across the water! Soon the two families meet the planet's natives, but they aren't pleased by the humans' presence. The aliens challenge them to a contest. If the humans win, they can stay on Terranu. But if they lose, they must leave immediately. It's up to the young friends and their special powers to win the contest. Will their families be forced to leave the planet forever? Or will the humans and aliens learn to live together in peace?