What to do?
 

Jr. High, you can tell the kids don't really know a lot about what is going on.
Team A scores, team b doesn't come and take the ball out, but one of the little kids from Team A jumps out of bounds and takes it out and before any whistle or anything, team A shoots it in their basket again! What is the ruling on this? Besides the officials need to be better noticing who is taking the ball out before it comes in!
After this happens is there anything you can do about it? Rule #?? Sure it could happen in a higher level too, but probably on purpose at that level.

There's a specific case play on this. Erase the points and any common fouls that occur during the mixup. Put consumed time back on the clock, if known. Issue a DOG warning to Team A for interfering with the ball after the goal. Give the ball to Team B for the throw-in.

If you think it was on purpose, do all of the above and assess a T to Team A.

It's case 10.1.8.

Perhaps 2-10-1e could be a friend.

I've never been in that situation where it was actually inbounded, when a wrong kid tried to pick it up, I just said leave the ball where it is please.

Better to have this learning experience at that level than in a HS game.

For Coaches And Fanboys Who May Not Have A Casebook ...
 

10.1.8 Situation: Immediately following a goal or free throw by Team A, A1 inbounds the ball to A2 and A2 subsequently throws the ball through A’s basket. Ruling: The following procedure has been adopted to handle this specific situation if it is recognized before the opponents gain control or before the next throw-in begins: (a) charge Team A with a technical foul; (b) cancel the field goal; (c) cancel any common foul(s) committed and any nonflagrant foul against A2 in the act of shooting; and (d) put “consumed” time back on the clock. Comment: If there is no doubt the throw-in was a result of confusion, the entire procedure would be followed except no technical foul would be charged. This procedure shall not be used in any other throw-in situation in which a mistake allows the wrong team to inbound the ball.