I don't think anyone is saying that it won't benefit children (at least not initially), the point is that the cost of doing so is high and it could easily lead

I don't think anyone is saying that it won't benefit children (at least not initially), the point is that the cost of doing so is high and it could easily lead to further costs which don't benefit children at all, perhaps even harms children. A good example is the argument for mass surveillance. Sure, if you know what everyone is up to at all times, you're probably going to be better at catching the baddies, but the loss in rights to everyone innocent is arguably unfair. To take it to its extremes, if you're goal is to simply put as many bad people in jail as possible, put everyone in jail.