A good replacement for regular rice is cauliflower rice. It looks and tastes a lot like rice and it may satisfy your child’s craving or need for the real thing. Hopefully he won’t even know it’s different.
You can purchase cauliflower rice in many health food stores. It’s often found in the frozen section. Be sure if you purchase it that it’s organic and doesn’t have any fillers.
You can also make it easily yourself at home. I found this website with good instructions, https://www.loveandlemons.com/how-to-make-cauliflower-rice/. She also has recipes for broccoli rice and zucchini noodles.