I just had a barny with my wife over this... Yes, it's scary; but it's all hype and the only real answer is to educate your kids far earlier than you think is necessary.
Like airplane crashes or shark attacks, you're hearing about this because it's sensational; not because it's common. Here are some numbers:
About 3 or 4 children worldwide have been linked to hurting themselves with the momo challenge over the past six months.
Today, about five or 6,000 million unique videos will be watched on youtube.
About 3 our 4 people will die on the road TODAY as a result of car accidents in Australia. Another 10 odd in California and another 10 in Texas.
There are about 20 million people in Australia, 30 million in Texas and 40 million in Cali.
You can cherry pick statistics to say what you want, but I think we can agree the chances of your kids getting caught up in the momo craze because of some random video on youtube
is pretty bloody small.
Given those statistics, here's my advice for practically ensuring your kids
won't be exposed to the momo challenge:
Let them loose on youtube completely unrestricted for the next 24 hours. ... and how to give them the best chance of
being exposed: Let them sit next to you all day while you listen/watch/browse the news and talk among your social groups on facebook.
Now... all that said; if they won't do something stupid because of the momo challenge, at some point they will do something stupid because of the Birdcage challenge, the Keke Challenge, the ILS Challenge, the Tide Pods Challenge, the Planking thing, the Investing in Bitcoin thing (that one got me, and I'm 37) or the Nigerian Prince, IRS pre-payment or donate to PETA scam (just to be clear, there's nobody pretending to be PETA that I know of - if you donate to PETA, you've been scammed).
You can't shield them. You can only educate them, and accept that they will do stupid stuff from time to time; you can only hope to minimize that, encourage them to stop and ask themselves if it's a good idea, and teach your kids (/self/wife/parents) about recognizing and avoiding
Escalation of commitment.
I let my kids who are six and three loose on youtube with about the same amount of supervision that my wife gives our kids a the local park.
Her trust in the children in a public place scares the shit out of me, and my trust in them on the Internet scares the shit out of her.