I think all of the things you mentioned would work fine in a Gamepack focussed on Childhood. It should also include many more child-child and child-toddler interactions than we have now, like all the games that child sims in previous games could play (like Mary Mack, tag, cops and robbers, hide and seek, etc) and the teach a nursery rhyme interaction that existed between children and toddlers. (Actually, I think those social interactions should be added to the basegame, not come in a pack).
Any child centered GP should also include (as essential elements for me) the bake oven, the bake sale table and the lemonade stand for children, and the toy xylophone and (small) teddies for toddlers. I would even like to have the music boxes from Sims 3 back; they were very nice. Some new interactions and toys that we've never seen before might be nice to have too. I would certainly buy such a game pack in a quick minute.
But what I want most of all is a Generations-style Expansion pack which adds all kinds of content for the neglected life stages in the Sims 4 (babies, toddlers, children, teens, and elders). Preceding it should be a patch freeing the babies from their bassinets (as some have already suggested). It could include the activities and events for children that you mentioned but could also include teens in some of them, and add unique hobbies and events just for teens (proms, etc) and elders (bingo, bridge, etc) too.
It would also be nice to have some of Generations' other best features back: the stroller (for both babies and toddlers), the sleeping bag, the ability to make home movies and play them on the TV, the playpen and walker (store objects in the Sims 3), and/ or the baby swing and floor mat (store objects from the Sims 2), the bachelor/bachelorette party with an exotic dancer, baby showers, the elders' canes, the show family pictures animation (so cute) and of course teaching teens to drive. If they finally added the ability for kids to ride bikes into the game, they should also add the ability for older sims to teach them to ride a bike; toddlers could get tricycles.
