Get them to stand in pairs, and put markers on the ground to designate a set distance that each pair should stand apart from each other (this can work with ANY number of pairs!).
Have one ball for each pair, and when you say ‘GO’, each pair attempts to complete 50 catches before any of the other pairs. If they drop the ball, they go back to zero and start again. First pair to reach 50 wins.
Once you’ve had a couple of goes at racing 50 catches, get the pairs to catch with their right hand only, and the first to 30 wins. After this do the same but with their left hand only. You can run a ‘team series’ whereby the pairs score points for winning in each of the rounds.
Instead of catches, you can test the players with some different feeds which are appropriate for cricket. Try getting them to roll the ball on the floor to each other, or to feed half-volleys. Or they can practise catching with their fingers up by having the feeds at shoulder height.