how old is the kid? If he is very young, I would just let it go. You could always bring the director to make him move if you wish.
Tournament kid player cheating what should I do?

He isn't cheating.Moving a pinned doesn't mean he is breaking the rule exactly.Maybe he didn't know it was pinned to the king.

There's always this kid who moves a pinned piece somewhere and then changes his mind and says adjust. What should I do?
Have you explained the rules to him?

I do think it depends on his/her age. If they are fourteen, I might call the TD--that's old enough to know better, and since the overall tournament result is impacted, it affects more than just you. If they are six, I'd probably let it go but try to figure out who is their coach and mention it to them as something they might want to talk about without pointing any fingers.

He isn't cheating.Moving a pinned doesn't mean he is breaking the rule exactly.Maybe he didn't know it was pinned to the king.
Also, it's possible to move a piece pinned to the King. If White's Queen is on c3, nothing on d2, his King on e1, and Black plays Bb4 with a black pawn on a5, and White touches the Queen, he still has legal moves with it, Qd2 and Qxb4, so even with an absolute pin, there may still be legal moves. If there is even one legal move with the piece touched, it must be moved.

There's always this kid who moves a pinned piece somewhere and then changes his mind and says adjust. What should I do?
Are there touch move rules in place? If so, pause the clock and call the TD over. Even if it's a child, that's how they learn. Always giving them free passes and take backs will make the learning process a lot longer. When the consequences are severe, he'll learn quickly. Also, to always claim it's adjusting if, to you, it's very obviously not, is just a flat out lie then. Mistakes are mistakes. If he doesn't own them, then you're encouraging him to be a cheat.
Does not matter the age. Call the TD. I have told me kids to raise their hands if their opponent is not following the rules. Does not matter the age. After all this is a tournament. Everyone should know the rules before they take part in a tournament.

Does not matter the age. Call the TD. I have told me kids to raise their hands if their opponent is not following the rules. Does not matter the age. After all this is a tournament. Everyone should know the rules before they take part in a tournament.
That's awesome parenting in my opinion. Kids need to learn that you shouldn't make decisions with the expectation that they can just take it back if it doesn't work out.

Is the piece pinned to the king? If so, the move wasn't legal anyhow (most likely). But, if someone grabs a piece and then later says adjust, that isn't an adjust if you're moving it around the board. TD should be called and opponent put on notice.
There's always this kid who moves a pinned piece somewhere and then changes his mind and says adjust. What should I do?