A cartwheel is certainly not the most difficult skill a child is ever going to learn on floor but every once and a while we get stuck for ideas. Here are two of my favorite stations to teach beginners a cartwheel. Both of these drills have been around for ever so I can not really give credit.
I absolutely love the semi-circle idea. Thank you for sharing! I rely heavily on cartwheels down “cheese” mats as well, helps with the momentum required to get the feet over the head.