The warm up, can be done by kids aged 7 and above. They can practice that. The general mobility, is also the same for children.
Unfortunately, you can't warm-up and give attention to flexibility in 30 minutes. Children should not be stretching deeply before a class. They should warm-up and 30 minutes is a good length for warm up. Flexibility must always be slow and attentive. So start with just the warm up and mobility for your child.
It is not so different for children.