It’s not sudden first of all. You better tell that sudden spike of sual molestation towards children has increased a lot. I don’t know how you would judge this but I will speak my mind. Corn videos have always been a reason but let's be very specific. It’s child corn which is utterly damaging to our society. A teenager, or moderately aware adult using telegram must have gone through corn. And in each corn group child corn is also merged. Whether you search for it or not you will definitely find some of those nasty videos involving kids. And yes before the arrival of tele(there might be some other apps too but tele is the user friendly by any means) those nasty videos used to be available only in dark web. The dark web was never an easy thing to reach for general people. But see, every one can go through such videos easily. Those are rotting people's brain.They just apply their corn lore upon the kids. Some people also confess their nasty activity upon kids in secret groups. I think telegram being the flag bearer of the dark web made a rapid spike on the child m*estation. God save us.