**Disclaimer** I only coached once at coach pitch, but my son's travel coach from 8U until this year (14U) was very good with this kind of stuff, and this is one of the drills he had them do for the last 2 years...
Lay out 5 spots in a star pattern, with a set distance between points with at least 2 kids at each point. The drill begins when a player throws the ball to the player at the spot across from them and then follows the throw, the ball should work its way around the points in the same kind of alternating pattern as tightening lug nuts. The distance shouldn't be so long that they can't run to the spot they just threw to and be ready to receive the throw back when the pattern returns to their spot, but long enough that they have to make good throws and still have to run to get to the spot.
The coach used to run that drill with them until they completed a set number of throws and catches without a drop.
One of the things that seemed like a problem at the time was that they would spend 80-90% of their practices doing throwing and situational fielding drills, but if nothing else they were able to keep games close with their defense, even when facing superior teams. I don't know how you split your practice time between fielding and hitting, but baseball is so much about repetition that maybe it will take a few practices of only fielding and throwing to bring them around.