Yes, being able to accidentally cause $800 overages is terribly anti-consumer.

After it continually happened to people roaming, the EU by law instated a cap where the operators need to request an SMS confirmation once the overages hit a certain cost.

For domestic data, I can't remember the last time I saw a plan that didn't just cap your speeds once you hit your data cap.

I wouldn’t say its the phone company’s fault directly but did they even try to contact your friend in any way to let them know that their bill is now 2, 3, 4 or even 5 times bigger than usual?

I mean, why should they? Most phone companies allow you to set budgets, I do not see this as an issue with the phone company in this scenario at all. As other people have said, parents should be monitoring their kids spending (if at all), most stores have an option to require the password - I do not see why this is not enough.

In this case it's a roaming surcharge not the kid spending money in the store.