I think this would be most successful if it were focused on animations. A lot of the DLC has new game mechanics, new objects, but reused animations. But a lot of the oft-suggested kid play interactions and baby stuff require extensive new animations to be any fun. Animations take an investment of time from different staff than the ones who invest time in coding new game mechanics.
But then, I think if the animations are done well, there wouldn't be much needed in the way of new mechanics, and only a small amount of work in creating new objects. I wouldn't mind paying $40 for a full suite of baby and kid content that included babies who could be carried around, parents sitting in chairs and talking or listening to music while holding babies or toddlers in their lap, kids playing at least as many kid games as Sims 2 had, kids and parents playing catch and dancing together (and while they're at that, it wouldn't take much extra work to make a dance together animation for teens and adults, maybe that could be the basegame patch that comes with the EP!)
