Yeah, apparently those Kinder Surprise egg opening channels (such as DisneyCollector) make tons of money off of their videos. Same with those unboxing channels that, well, unbox new toys.
But I think the reason why little kids like those videos so much is because they're just relaxing and kinda mesmerizing to watch. Heck, I like to watch certain kinds of videos just to relax and unwind. That's why ASMRs are a big trend on YouTube right now.