On the year stretching from June 1, 2019 to June 1, 2020, Kaji is estimated to have brought in $29.5 million, outpacing the rest of the top five: Mr. Beast ($24 million), Dude Perfect ($23 million), Rhett and Link ($20 million) and Markiplier ($19.5 million), though they're all probably still pretty happy.
Kaji's channel, Ryan's World, snagged 12.2 billion views between the Junes of 2019 and '20, doing so off the backs of what Forbes describes as "DIY science experiments, family storytime and reviews of new toys.'" While views of said videos pull in major dollars for the youngster, it's noted that the bulk of his fortune reportedly comes via licensing deals on more than 5,000 Ryan's World products, like action figures, clothes, and walkie-talkies. He also has a series that pairs him with the previously unquestioned authority on what kids like (see: Nickelodeon) called Ryan's Mystery Playdate.
Note that Ryan is not even the only person on the list with a single digit in the age category. At the seventh spot sits six-year-old Russian YouTuber Nastya ($18.5 million), whose channel features *re-reads with confused look on face*: "her and her father playing with legos, doing household chores and explaining viruses."
As for those making up the rest of the top 10. At No. 6 is Preston Arsement ($19 million), and then 8-10 are: Blippi ($17 million), David Dobrik ($15.5 million), and Jeffree Star ($15 million).
The whole group can boast of subscriber counts ranging from Star's 16.9 million to Nastya's...whoa, 190.6 million, and past year view counts ranging from Star's 600 million to Nastya's (whoa, again) 39 billion.
For general breakdowns on what they do/what markets they've cornered, you can check out the whole list over at Forbes.