|These booklets are handy!|
Form two teams. Number or otherwise organize the players so that a serving rotation is established - you don't want the same person serving all the time. Teams play out regular singles points against each other. Whichever team wins the point earns the letter 'C' and continues serving with the next player in rotation taking the next turn serving. First team to spell out 'Champs' wins.
Easier: have players throwing ball instead of hitting with racquet. Or use foam or lower compression balls.
Harder: only one serve allowed - no second serves. Or establish a minimum number of rallies to be completed before points can be won. This second may remind you of the 3 Monkeys drill which could be incorporated here also. You could establish a minimum number of rallies, or have them hit a particular shot like all forehands, or some combination.