This is a "tricky" subject.
Puting you finger on something conductive which is stuck in the socket's "Live" contact tube is, in itself, not generally going to result in too much of a shock
unless another exposed/damp part of the body is touching something that is solidly earthed.
That could happen if the kid's other hand was on something like a c/h radiator which could well be next to the socket, and that case the shock current would run from the tip of one hand to the other hand, i.e. straight through the heart. That "really hurts" as I know from my own experience when I was touching one end of the metal chassis on an opened-up amp with one hand and then the fingers of the other hand accidently touched the backs of the pins of the mains switch at the other end!
Also, a kid is physically much smaller,and the skin is softer, than an adult , and thus the resistance is likely to be much lower and both of those factors are likely to increase the shock current - and that's exactly the reason why mains sockets in this country, and also in most parts of Europe, are (and have been for many years), "shuttered" to reduce the possibilities of kids sticking "things" in the contact tubes!
Personally, I think that this sort of advert is, frankly, stupid!