Guest from the Future (1984)

Sixth-grader Kolya Gerasimov discovers a time machine in the basement of an old house in Moscow and gets transferred into the 21st century, where he is allowed to look around. He accidentally witnesses two space pirates arrive from Saturn and try to steal a device called a "Mielophone," which can read thoughts, from Alisa Seleznyova, a girl that performs experiments with this device and animals. Kolya manages to save the device from the pirates, and he takes it back to the 20th century--followed by Alisa and the pirates. Alisa knows where Kolya studies but doesn't know what he looks like; the pirates saw him but know nothing about him.