Looking from a negative view, wouldn't this be a form child labour? These kids should be enjoying their childhood like playing video games, sports, toys and/or marbles.
I am not against getting kids to ask for donations, but wouldn't those kids be force to do it enjoy asking for donations through their time from Secondary 1 to Secondary 4? I agree that this would be a better time to instill these values (im not saying starting early is not good...but in one scenario: doing it too much would create a sense of boredom and resentment towards the parents from the feelings of being forced to do it (depending on parenting)) in comparison to the kids' younger days, when they may not even comprehend what is going on.
Other factors may also come into play such as belief of karma, religion, influence of friends, preservation of 'face' from friends and relatives, etc.
Charity Singapore