Just how many martial arts places have you been to, looking at your posts across different threads you must have been in hundreds of them?
I've taught children martial arts, horse riding and am also a Girl Guide leader where the youngest girls are 5, children can learn easily. Of course everything must be age appropriate to get the best from their lessons but really, children can learn martial arts at a young age. Whether they should is up for debate as people have different views on it from various points of view but not because children cannot learn. The argument against is whether they should be taught at a young age and grade so that you have young blackbelts while the argument for is that the children learn the ethos of martial arts to take forward into adulthood, neither argument says that children cannot learn.
Correct, good that you remind me though.
The training environment and training structure I saw children in, were the same as for adults, this might be the reason why they were not able to follow or concentrate as much as we adults did. I've got no children, so I don't know much about it. However, to answer your actual question, I've been to around 70 maybe 80 different martial art schools, in 50 of them I were just a guest for a couple of weeks, in some others I learnt for months or even years to adapt and gain as much knowledge as possible.