so basically you are focused on quantity...that's great. I am more focused on quality. To each his own I suppose.Now that I understand and accept your point, I would ask you to do the same with mine:
although the parents may feel better about the differences and the quality of the activities "back home" or "somewhere else", Hong Kong as just as many opportunities for exploration and exercise as any other city.
In fact, I would argue that comparing with other big cities (Manhattan, London, LA, Paris etc etc), Hong Kong has many more varied activities for kids, closer to the city and these locales can be reached more conveniently. These activities may be different but they are equally beneficial to the growing needs of children.
My most important point is : it doesn't matter how the kids get their exercise. The fact that they do and have the opportunity to do is more important on how big or how green the grass is.
If you are not near the bike paths, then go for a hike. The path is too far, go for a swim. You dont like swimming, go climbing indoor or outdoor. Horses? Football? Rugby? Netball? Sailing? There are many many choices at very affordable costs.