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This can happen when your driver ignores the vsync settings of the game.  Try switching on vsync in your driver settings. What platform are you on?

Thanks for that fast answer! I just updated my previous comment before I saw yours: vsync changes nothing if I force enable it in my graphic settings. Using Windows 10, up to date as well as GPU drivers.

Could you send the game log file to mail@playkids.ch?  Maybe there's something hidden in there.

It should be here:
C:\Users\<your_username>\AppData\LocalLow\Playables\Kids\Player.log