As for how much it is appropriate to buy critical illness insurance and medical insurance for children, it depends on your financial situation. As we all know, the higher the premium of this kind of insurance, the higher the amount of insurance that can be obtained and the smaller the economic loss. Therefore, if you want to give children higher protection, you can raise the premium appropriately, but the total premium insured for children should not exceed the total premium insured for adults as far as possible.
Further reading: How to buy insurance, which is good, and teach you how to avoid these "pits" of insurance.