If the mechanic of how the children are added to the residence is too much of a complication, perhaps the proposal could be stated with an explanation of which aspects are the priorities. For example, my reading of the idea is that
First priority is having an option to add children to the city
Second, have the children attached to a specific house
Third, interact with streets or other children
Fourth, require no additional space
With explanations given as to why each priority's requirements is preferred over existing methods of implementation, like street options and new additional stand alone buildings. Wouldn't the amount of effort expended by developers be higher if it is a very popular idea or if there are convincing arguments as to the value it brings to the game? If the demographic for this game is as described below, the building or upgrade that enabled children would be a "must have" for many, in my opinion.
Elvenar is not PvP oriented and has a different target group, it targets Females (and males but females first) in the age 35-60.
There are alternative implementation methods that the developers could choose, for example, if a compromise on requiring additional city space must be made, maybe children could appear in a backyard/frontyard/sideyard building that is part of a set with residences, that generates no resources unless placed as a set. The "yard" addition/link would increase culture and decrease coins.
If the "yard" could evolve and the children age through artifacts or diamonds, I think that would be very popular as well. I could see there being more incentive to play the Spire in order to obtain diamonds in order to add and evolve children.