You’re supposed to be “mean” (it’s not mean at all) in this case.

Tell them to stop following you around or talking to you, nicely, exactly once.

Then, if they don’t comply, you are probably dealing with a troll who enjoys annoying people. Children especially are prone to that. You have to stop doing anything interesting for a bit, just go afk, make a tea or whatever, and wait until they get bored and move on. Then you can resume playing.