Yeah, knocking out pain receptors in children seems like a very bad idea. Pain is unnecessarily harsh if you already have a strong interest in preserving your body; then all you really need is to know that you're doing something bad to yourself, and that's more than enough reason to stop. But for those who are not yet sufficiently rational, like (most) children, it's probably not something to be messed with without serious consideration.

The team's first research subject, a 10-year-old boy, was well known in his community for street performances in which he placed knives through his arms and walked on hot coals. Despite tissue damage, he apparently felt no discomfort.

It sounds like that kid has some of the worst parents in human history. How do you let your kid get a reputation for self-mutilation and not, y'know, stop him?