I understand where you are heading, but I have to remind you that we already have 8 lifestages and out of those 8 only young adults and adults are not ultimately ignored. Just a reminder, we only got two kits for kids, with another one containing one outfit for kids and no kit for toddlers and infants. Kids, toddlers and infants got almost zero outfits and activities in latest EPs, with teens only being better, because for the game they are basically adults, so, they can wear all the adult outfits and do a lot of adult activities. And don't even let me start with elders.
With that said, I'd rather for Maxis and EA to concentrate on the lifestages we already have, than creating new one that, after the initial pack dedicated to them, will end ignored like the rest.