I’ll leave the silly comments about kids alone, except to say mine are sitting quietly in the Marriott Sky City lounge now while a bunch of loud men shout at each other, making each other table of men shout louder and louder. It’s hilarious.
As for one guest, hah, I love the arm chair revenue management around here. I have a suite with 5 occupancy allowed. I’ve never had a property seek to limit us in this manner and doubt they would if you complained. Your assumption that these kids are somehow “freebies” coming in on a parent’s upgrade to a Club room suggests you’ve never bought a suite or Club level room before in your life, where this is an advertised benefit and not something Marriott is going to take away because some “upgrader” is annoyed.