Could they go the other way and analyze join events to groups or something on their own networks to find groups? I guess the issue then would be that they're mo

Could they go the other way and analyze join events to groups or something on their own networks to find groups? I guess the issue then would be that they're monitoring every group? I can't imagine these people are writing something like "child porn in this chat --> <whatsapplink>". I haven't the faintest idea how people who're interested in that sort of thing're finding these links. Definitely a problem which seems potentially intractable to me, although perhaps more familiarity with the platform and the offending chat groups would help (or... more likely... leave me rather disturbed).