OK; beyond the fact that we can now take a phrase and print it on pretty much anything that can hold still. (It will therefore not be stamped on an actual baby’s bottom.)
Call it bonding, call it a little harmless passive aggression toward the new ogres, the parents — the attitude is something like, I have put in my time as a disciplinarian, and now, dammit, grandmas just want to have fuu’uuu’un!
Obviously, this approach does not work with toddlers, who cannot be trusted to keep a secret. It’s most appealing for the primary school set, who can appreciate the thrill of a rule broken, and who are not yet involved with prohibitions concerning things like porn or drugs. The unauthorized dessert, the late bedtime, the movie with the wrong rating: what, after all, is the harm?
This end run around the parents may also be related to the fact that we, the disciplinarians of yore, are likely at a time in our lives when options are more likely to be closing down than opening up. So kicking up our heels can feel great. Our grandkids become our partners in family-friendly vice. Just a little bit like Vegas, baby.