Well, in this particular case with adults you can make the (in my opinion very flimsy) argument that they're at least in principle capable of understanding the

Well, in this particular case with adults you can make the (in my opinion very flimsy) argument that they're at least in principle capable of understanding the ramifications of who they give their data to and the websites they visit etc. A child on the other hand can't be expected to exercise good judgment and discretion about who they should and shouldn't give their data to. The landscape is just too complicated. (Of course, the aspects that are complicated are ones that adults don't understand anyway.)