Attention, Turtle!(1970)

Original title: Внимание, черепаха!

Two curious first-graders decide to steal a turtle named Rocket from a living corner to conduct a risky experiment — they want to put it under the tank in order to check the carrying capacity and strength of the shell. But their classmate Tanya is smarter than her friends: with the help of adults, she manages to organize the rescue of the unfortunate turtle.