Just because a lot of kids are using it doesn't mean it has 1.2Bn downloads. That's a lot of downloads.
Gmail is 10 years old, for context, and it's ubiquitous for basically the entire population, and it has barely 4 times that. When you account for the fact that most Gmail users have gone through several phones and downloaded Gmail several times, it seems pretty suspicious that an app only for kids has 1.2Bn downloads -- when it's possible close to the entire Android mobile users that use Gmail -- which comes pre-installed on like ~60% of phones in the world.
I'm pretty sure these numbers do not include the Chinese market at all, since they don't have Google Play Services. A lot of Tiktok's users are supposed to be in China.
If these numbers are supposed to include Chinese users, I'd take that with a double grain of salt. For the same auditing reasons, we have no reason to trust any download counts that come from a Chinese company.
If these are supposed to be only iPhone numbers (which AFAIK include Chinese downloads), that's SUBSTANTIALLY more suspicious. There definitely aren't ~750Mn kids with iPhones. And the numbers that would imply in total are completely unbelievable.
At a previous company, we did a marketing campaign with TikTok. They claimed that more than 65% of their users are under 25.