I think that not only OTD kids are very sensitive. A lot of people today are extremely sensitive.
Sensitivity in itself does not cause people to go OTD. There a lot of frum kids and adults who are sensitive. In fact, because of my childhood where I was constantly critisized and degraded and tried to be forced into a certain mold, I used to be extremely sensitive if someone ever critisized me.
I made a conscious decision not to fous on what others think of me, but just to focus on doing the right thing. That took care of my sensitity, B”H.
Critisizing and degrading or spoiling children are some reasons that cause children to develope hypersensitivity. But also some children have geneticaly predisposed sensitive characters.