Honestly, Youtube has no idea the percentage of total views that are coming from kids under 13 because kids under 13 don't have accounts. Many channels think that their analytics page provides information on the age of the viewer, but the data is garbage because the viewer is most likely not the person attached to the account that is logged in. I believe close to half of the views on Youtube are coming from kids under 13, but there is no way to determine this.
Youtube has now penalized content creators that were actually making appropriate content for this age group by tweaking the algorithm. The kids are still going to watch, but they will now watch content designed for someone 13 or up. I just checked my daughter's tablet to see the suggested videos (she is 7). Youtube suggested a kid friendly video from the Ellen Show, a video of a lego car from Mr. Beast, a video from Inside Edition called "teen posed as a doctor", and PewDiePie 100 million youtube award video. Not one single video suggested from the kid channels that she likes to watch like tic tac toy. It is obvious that Youtube is not suggesting kid content anymore.