But "we" are not in control of "the server". I agree though it's worth doing, adult content should be tagged as such. But it doesn't handle the case of non-compliance.

"We" are not in control of the server or phone client or tablet applications. Should the 5-eyes or 9-eyes countries pass a law to use RTA headers on servers and look for the header on user-agents that should suffice to get basic coverage for kiddos by default and parents can disable the checks if they so desire.