I think it is fair to say they need more. There is not much reason to play them with the base game other than aging and aspirations/skill boosts. Toddlers get play dates and playgrounds with Toddler stuff, kids get voidcritters and the puppet theater in Kids Room, and all three stages get character values and related play with Parenthood. However, in the grand scheme it still is not that much, especially with the limitations on other content.
Kids cannot garden, cook in any way, walk or bathe pets, etc. This is on top of having practically nothing else to do beyond homework, dollhouses, toy boxes, the theater, and void critters. I suppose they have knitting, too, now, but even with adult skills they are limited. It usually is not worth focusing on a child character for me. I get bored waiting for their school obligations to be done and then have nothing to really do with them that I could not do better and easier with a YA. Teens are pretty well the same. Plus their mood swings can be fairly annoying and are not enough to separate them from YAs.
I like the toddlers in Sims 4 the best, though, but I would not turn down making any of them better.
