I think because kids accounts literally exist and don't allow this. The did didn't set up a kid's account for his... kid. Google had safe guards and he used exactly none of them. I'd blame Google if the kid subverted the controls in some way, but doesn't sound like he did. Either the dad let the kid use the account, lied on account creation for the kid or turned the controls off because they were too annoying (this one I have seen a lot). At a certain point we have to be responsible for our own actions.