Exactly. I'll bet when some parents found out about the warning about Momo, they got really scared, and SHOWED their kids the the warning video, asking their kids if they had seen the video of Momo. Because they were freaking out, their kid got freaked out and started crying. Not knowing why their parents were freaked out all of a sudden, only that it was over the Momo video/image/pic. So, then their parents think it IS the Momo video/image/whatever that is freaking out their kid. Only their kid can't articulate WHY it is Momo, they just know they
should be freaked out by it - because their parents are.
Then the parents take the kid to the ER as they are all freaking out. And when the doctor asks they why the kid is freaking out, they say it's Momo. Even if the doctor asks, "Did YOU show him Momo or did he come tell you on his own? The parents probably said, "Of course I showed him Momo. I had to know if he saw it. And he did. He freaked out the moment he saw her." When actually he freaked out because his parents were freaking out.
And as for kids saying they saw Momo in a video. Kids show each other things. Probably some of them have seen the
warning videos about Momo. Their parents may have shown them. So they show their friends. And then the other kid tells their parents they saw Momo in a video and they are scared. But, they aren't being clear that the video is a
warning video. (The kid might not know himself that it was a
warning video he saw.) The parents just think Momo popped up in
a video the kid was watching.
It reminds me of an interview I saw recently with Daniel Radcliffe. He was asked what it was like the first time he was mobbed by Harry Potter fans and was it really scary for him? Daniel said it happened when he was rather young, like at about age 6. They had come out of an event and the sidewalk was mobbed with hundreds of HP fans. Security was in front of him & his parents, pushing their way to get to their car. People were grabbing at Daniel. His mother might have lost her hat. He had a sleeve ripped. They finally get into the car and shut the door.
Daniel said he doesn't know if his parents had talked ahead of time and planned their reaction to such an occurrence. But, they both started laughing. Then shrugged, and said, "Wow, that was really weird." Daniel said because his parents hadn't freaked out, he hadn't either.

If they had acted scared, he would have too. To this day, Daniel and a few of the other HP actors maintain that HP fans are some of the nicest & safest fans anyone can have.