With my 5 and 6 year old boys T-ball team, we tried having the boys throw balls back and forth to each other at our first practice. It went badly because no one can throw well or catch well.
The players were afraid they were going to get hit by the wild throws or the thrower was afraid they would hit the receiving player with the ball which resulted in wimpy throws going back and forth. Very few balls were caught and we spent a lot of time running after stray balls.
At the next practice, I came with a bucket of plastic whiffle balls for each kid (ten per player). We practiced good throwing technique by throwing the balls at traffic cones instead of each other.
No one was afraid of getting hit and everyone got to throw a lot in a short amount of time. The boys enjoyed refilling their buckets after everyone was empty. I did not have to pick up any of the balls myself.
It worked really well. I recommend giving that one a try. We are going to do it again at our next practice.