Adult equivalent of baby toy phone is a phone (landline, cell, whatever). You might as well argue that people who as children were hooked on baby phones will use a phone as adults. Which is trivially true because everyone will use a phone as adult.

Same thing with chat. Children addicted to children's facebook chat will use some form of chat in the future because everyone will. They are already using chats. LoL in-game chat for example. Recently 10 year old from my extended family thanked me through Clash Royale in-game clan chat for some random promotional stuff my girlfriend gathered during shopping and passed to him through her brother.

> ... kids attached to a system that they don't fully understand.

This pretty much describes any system kids are attached to and many systems adults are attached to.

> it's just a chat app, but, given that facebook is a business, its ultimate purpose is to make money.

So? Same goes for anything. TV, print, games, sports, clothes, even partially education if you live in US. Should you avoid attaching your children to all of those systems?

The only thing you should do for your children is to make sure Facebook is not the only chat app, that some better chats can be created and alive even if they don't have as much money for lawyers and greasing the wheels as facebook has. You can do that by coercing companies to disclose details of their technology or at least stop helping them protect it. You want to create new chat product? Fine, but you have to release protocol that your chat app uses so anyone can write a client. Your protocol docs are outdated? Company gets a fine of amount associated with their revenue, operational costs or whatever number that correlates with their success that their accountants can't hide.