The players are lined up, single line, behind the baseline. The coach, having a basket of balls nearby, is on the opposite side, inside the service court.

Drill:
The coach feeds a ball to the first player in line. She will try to hit it over the net and inside the opposite court (singles only). If done successfully, she will move to the end of the line.
Next player takes her turn and so on.
But, once one of the players misses the shot (hits the net or out), that player is out of the game, and from there on, each player will have to hit 2 balls in a row over the net and inside the opposite court.
Again, once a player misses she gets out of the game and the next remaining players will have to hit 3 balls consecutively in.
And so on, with every player who leaves the game the next players are being added an extra ball that they will have to hit in; until two players are remaining.
The last two players just compete in the first one to miss, being fed only one ball at a time.

Note:
This game will give young players a sense of a pressure competition in a friendly way.