i'll try to answer everything in a neutral way
now thinking back about it some toddler stuff can be added in basegame but not everything and watersliders won't have to be this big for both toddlers and for other lifestages
for children and latter stages it can have the watersliders like The Sims 2 had since we don't have normal watersliders in The Sims 4 yet and for toddlers it can have smaller watersliders (normal watersliders should be in basegame which we don't have yet like they have added pools in basegame later)
daycare in this case it can be optional like "Get To Work" careers and some other careers from other packs, i'm sure the team can figure things out and yes i'm aware we can create things from "businesses and hobbies" i tried them myself but won't it be more usefull if you can do daycare without having to stress out with your active sim the businesses get automatically closed if it goes to other lots? (i heard from others your business gets closed if you visit other lots or even other worlds if you own "businesses and hobbies" pack)
besides i bet lots more items and activities get added in a toddler based pack, it won't hurt to add more things for toddlers like playgrounds for toddlers only to name one
as for the toy store it won't hurt to have some kind of a shop which you can buy some toys for the toddlers without running a business from either "get to work" or "businesses and hobbies" it's kinda like saying "*you can run a library with businesses and hobbies pack*" if you ask me but library was a thing as a venue type since the very start so it wouldn't hurt to add some kind of a toy store without running a business (i want something similair to The Sims 2 you visit the venue type only to buy some items, it was a thing in The Sims 2 back then)
as for the traits it may or may not be too similair but i want more toddler traits either way because we have so little options not everybody is the same, i just couldn't think up with other traits
as for the playdate i've heard it's there and i'll try them out someday but for the basegame update it isn't just about toddlers, it's literally the whole household i was talking about, not just toddlers, more similair to The Sims 2 incase you haven't played that game, The Sims 2 had the option with the land phone to invite each of the household, i miss that to be honest
as for "it should be in other packs or basegame" you can say that with most of the packs and maybe even kits so knowing EA they makes other packs that should be in an already existing packs