A match ends at five points, but there is no losing screen. Both friends cheer on the court and the only button says 'One more'.
A grown-up sets the speed. Three steps, behind a three-second hold. It starts on the slowest; move it up once they are used to it. It is not in front of the child on purpose - they will choose the hard one and not know how to get back.
Nothing is saved. No account, no sign-in, no record of anything.
No ads, no purchases, no timers. Nothing here makes it hard to stop.
What you need
A browser. A tablet held sideways is best, and a keyboard lets two play together.