I think that is a very personal question. Parents have to address that as they're looking at providing guidance to their children in terms of proper nutrition.
If you're asking me, I have two boys; one of them is four, and he doesn't drink pop at all. The other is seven, and he gets a half can a week.
I think there is a broad recognition from a number of stakeholders that there's a challenge in northern communities. I would argue that in every jurisdiction in the world, soft drinks are less expensive than milk. The general reason is that with milk there is an animal involved, which has to be cared for. Additionally, in Canada there are pricing schemas that dictate how milk is priced. That is compounded by the complication of getting fresh produce into remote and northern communities. I don't think anyone disputes that it's an issue that needs to be looked at.
Do I have a recommended amount for a parent to consider for how much pop or soda their children should have? No, I don't, but I think it behooves parents to understand. Canada's Food Guide is a great example; it has a number of limit statements within it. There are alternatives out there in terms of no-calorie and low-calorie alternatives that have no sugar in them whatsoever.
The objective is that parents need to be equipped in order to make informed purchasing choices.