Do not get very nervouse, he is just a kid, and as long as you all have immigration visas to Canada, you all are eligible to land anywhere in Canada, the port of entry you reach first is going to make your landing procedures, but they will confirm in your papers that your destination is Quebec. For your son, he can land with you in Quebec with his FSW visa, but they will write that his destination is anywhere else other than Quebec
If for any reason, they refused to land your son in Quebec, they will land the whole family, and ask you to re enter Canada with him later from any other port of entry to land him there, and then you are free to go anywhere in canada.
It is not a big problem, do not be worried, and do not miss the deadline of your landing visa, go and land as soon as possible.