> While in absolute terms it's not any more ok to spy on adults than children, the idea of spying on children being more morally repugnant is based around the idea of children as innocent and by spying on then we're depriving them of that and allowing malicious actors to prey on that innocence (hey, now someone knows where this child will be, when, and most of the important things happening in their life; much easier to trick.)

This seems like a very mushy reason. I'm pretty sure the real reason is that children are not considered able to knowingly consent to many things - including contracts such as EULAs or TOS. Given this, a child is also not expected to be able make a reasoned decision about privacy tradeoffs.

The reason it's "ok" to spy on adults is that they can make an educated decision about whether they're ok with being spied on. I don't necessarily agree that this is true in practice, but I think that's the theory.