Yes, I found out what it is after I learned that he meant mental conditioning. That works on kids to some extent, yes. It's not brainwashing though as brainwashing is about changing someones established beliefs to something radically different than what they originally believed, kids have no established beliefs and as such are malleable in which case you can influence their beliefs heavily.
I doubt you could condition a human to kill for a cause through that though, killing is a fairly complex behavior. It's fairly hard to influence humans into a specific behavior through this. Most of them are involuntary learned responses, such as teachers hearing the bells ring after a class is over and they feel they need to go the bathroom, because that's when they have time to do it or people who feel an urgent need to get to the bathroom as they're approaching their home and take their keys out, the sound of the keys triggers the response.