The Sims 4 Toddler Stuff mostly delivers on this idea- with a handful of CAS objects for toddlers, a big variety of build/buy mode objects which you can use to build a playground with, and a new 'play date' event for adults and toddlers to attend together. We were all so excited to have this missing life-stage added to the game (for free, no less), but after a few months went by, fans were asking for more content for their little ones.
When The Sims 4 team patched toddlers into the game for free in January 2017, the Sims fandom was SHOOK.