I know this post is a few weeks old, but I thought I'd chime in anyway. My son joined the team last year, when he was 5 (and had been doing rec for about 9 months). He couldn't do a cartwheel to save his life. Forget straight legs. He couldn't even get the concept of turning his hips around to face the original starting point. Just kept facing forward and fell over every time. I have a video from last August showing him doing that. By his first comp in November, he could at least land the cartwheels, but his legs remained very bent. By states in March, it was exponentially better. He still doesn't have perfect form, but it is so much cleaner. For him I think it's a combination of general body awareness (or lack thereof) and a lack of flexibility. The improvement seems to come so slowly, but when I look at the progress he's made just in the past 4 months, it's amazing. Good luck to your son! He'll get it soon, and then he'll move on to the next challenge.
