My twins are 3 1/2. They don't have phones. But they will, and I'm terrified.
Looking at this list, I hadn't even heard of 7 of the 15. And of the 8 I do know of, I'm not exactly sure how 6 of them work.
I guess it's all about doing your research and being diligent.
The Seguin Police Department says these apps aren't inherently bad, but they could be, and you just need to be aware of what apps your kids are using and how.