Teens in the Universe (1975) on Netflix

Plot summary

The starship Zarya carries a crew of teenagers who were meant to grow up during a twenty-seven-year voyage. Less than a year of travel time brings them to the Shedar system, and remote sensing shows that one planet is very much like Earth. The expedition is manned by pioneers, the Soviet scouts. Three of the crew descend in a reconnaissance capsule and find the planet apparently abandoned. Fedya Lobanov, the extra member of the crew and a stowaway, meets strange human-like creatures, and they escort him and his companions into an underground city. There the radio link with the orbiting Zarya goes dead, and the landing party is unreachable.