But it turns out that they may be making even more money than you think.
AdAge recently published a ranking of the top YouTube stars according to their estimated monthly earnings.
The data was compiled by Outrigger Media, who focused on the top-earning channels in two genres: beauty and style, and food and cooking.
The top earner in the food and cooking genre is a channel called CharlisCraftyKitchen, which features videos of an eight-year-old named Charli sharing baking tips.
According to Outrigger's estimates, Charli's channel generates an average of $127,777 in ad revenue per month. That's taking into account YouTube's cut of revenue. The channel gets an average of 29 million views each month - in March, it had 29,133,270.
Charli began making her videos in 2012, when she was 6. Her five-year-old sister Ashlee also plays a role as chief taste tester. The girls have made tutorials for everything from Minnie Mouse Oreo pops to jello popsicles inspired by "Frozen."
Check out one of their videos here.