Here is one of the youth baseball fielding drills that my U8 team likes.   The focus of this relay is receiving the ball rather than throwing.

Baseball Relay Race
Objective: Get players to be in a good stance to receive the ball and to get it to the next player down the line as quickly as possible.

Skills: Receiving the ball versus catching.
Receiving = having the free hand close to the glove, so when the player gets the ball in the glove they can get it and throw it to the next player.

Also helps with footwork in that the players need to turn around to make the throw to the next player.

Variations: 2-3 teams with 4-6 players per team, start relatively close and work on close shuffling the ball such as the toss from short to second.

Then move the kids farther apart and to get the throws to the target (chest/glove), and even farther apart to simulate the cutoff relay throw.