I would really benefit from having an optional preschool for toddlers.
Usually I play one or two sims but now I am expanding my horizons and started playing with families. Part time jobs, odd-jobs and school lets me concentrate on different sims at different times since I want all of my sims to have friends and hobbies.
I would like to be able to send the toddler away for a bit during the day if my writer sim is writing a book or gathering plants. I also would like to see homeschooling in the game.
Just being able to influence which sims are are at home would go a long way in making families more enjoyable for me.