I guess the main issue is that families have lower disposable incomes. So, if people with lower disposable incomes can't afford something there are only two solutions: increase their incomes or decrease the costs.
Reduce the Costs:
The City needs to do more to make housing affordable. The best/easiest way is to ease up on zoning restrictions. The current zoning plan basically protects most of the City from any kind of intensification whatsoever. If you try to concentrate all residential growth into a few centers and avenues, maybe representing 10% of the City's area, it's not hard to imagine that costs will be higher than normal. (It also gives people an incentive to build McMansions. If you can't subdivide your property, the only way to make money is to build a bigger house).
With respect to condos, I'm curious as to how much of the cost is secondary. As in, in the RCMI condo thread, I read that a parking stall in an urban condo can add 20-40k to the price of a condo. If you add up the costs of building condos with massive lobbies (and foregoing potential ground floor rent), swimming pools, saunas, gyms, bowling allies, conference rooms and god knows what other "common areas" the additional cost per unit must be quite staggering. Other features like "podiums,""crowns" and soon green roofs must also add costs. Looking at cities like Hong Kong or Seoul, where large numbers of families do live in high density neighborhoods, the buildings
seem quite spartan. If we were serious about wanting people with low disposable incomes to move back to cities, maybe this would be a direction to look at.
EDIT: Mandating a certain percentage of "family units" probably won't do much. The problem is that middle income families for the most part can't afford to spend 500k+ for a "family sized" condo, or at least feel they would get better value elsewhere. Developers will either just consider them a "cost of business" and spread the costs over smaller units (making them more expensive) or try to paint them as luxury units for richer, childless, buyers (or both).