A small spinner that fits most child hands. 
so that Junior can be activated for some time on the back seat…

The design is made for 604 ball-barrings and 3 standard 6mm nuts. 

Just print it and push in the ball bearing and the nuts. The 2 middle parts may have to get a small amount of glue.  

The design is a Print in place, so no need for supports or raft, or brim.