1.   This is a stop the lead runner format.

How to Stop a Play
1.    To stop the play when runners are on base, an infielder possessing the ball must be in front of the lead runner and raise their arms so the umpire will call time. As well, another way is for the defense to get the ball to the player (pitcher) at the pitcher position and the pitcher (and only the pitcher) while physically located in the circle (at least one foot at the circle line) must raise both arms to stop the play. Once they raise both arms, they give up their team's right to make a play.
2.   Once the play is stopped, base runners will return to a base based on the following:
-   A runner between 3B and home will return to 3B if they are not at the halfway point of the base path or proceed to home if they are at the halfway point of the base path.
-   The lead runner determines the status for runners behind them. 

Overthrows
An "overthrow" is defined as a throw by an infielder to a specific base where an infielder is at the base and the throw gets past the fielder. An overthrow includes a throw from an infielder to the pitcher. An overthrow excludes throws from outfielders and excludes any throws to a base where an infielder is not on the base. Further, an infielder catching the ball then dropping it is not an overthrow.

Overthrow baserunning for 7YO Baseball
1.   A batter turned runner after hitting the ball from home to 1B cannot advance past 1B if there is an overthrow at 1B. All other runners may advance.
2.   If a runner going from home to 1B attempts to advance on an overthrow at 1B, the play will be stopped. All runners will be returned to their previous base without a chance to advance. 
3.    The play will stop on the first "overthrow" to a base or pitcher position.  At that point, runners can advance at their own risk to the next base. Regardless of what happens with the throw to that next base, the runner can advance no further. As an example, if there is a runner at 1B, the batter hits the ball and an infielder overthrows the batter running to 1B, that original runner at 1B can advance no further than 3B.

Overthrow baserunning for 8YO Baseball and 7/8YO Softball
1.   A batter turned runner after hitting the ball from home to 1B cannot advance past 1B if there is an overthrow at 1B. All other runners may advance.
2.   If a runner going from home to 1B attempts to advance on an overthrow at 1B, the play will be stopped. All runners will be returned to their previous base without a chance to advance.
3.   The play will stop on a second "overthrow" to a base or pitcher position.  At that point, runners can advance at their own risk to the next base. Regardless of what happens with the throw to that next base, the runner can advance no further. Regarding the original overthrow at 1B for the batter, the batter cannot advance on the original (first) overthrow but could advance further on a second overthrow.