What do you mean school visa ? You want to send your son to Canada at 3.5 years old for what purpose at that age ? Do you have any status in Canada yourself given even if possible which is probably not it does not guarantee a parent can accompany which I am sure is not what you are thinking ?
Others can comment as well but I would think the chances of getting a study permit for anyone under 5/6 is remote and even then there are requirements for having a custodian/guardian in Canada given unlikely a parent would get a visit visa if at all for any length of time to accompany.
As been pointed out. Getting a visa for a child does not guarantee that a parent can come to Canada with the child. Generally you have to get a Canadian guardian and that is why most are in high school.
