This is how I think toddlers should be in The Sims 4:

Toddlers would be controlable and have more than 2 emotions, unlike babies, they would be able to feel happy, unconfortable, sad, playfull and angry. Toddlers would automatically get a soother in their inventory which they could use in a variety of ways according to their emotional state, making them feel more happy.
They would be able to only drink from the bottle not sustaining their hunger for long until after a few days, after they got a moodlet saying "Busting Teeth" which would last for 3 days, after this they would be able to eat more elaborate food sustaining their hunger for long.
Toddlers would also be able to interact with objects like viewing them, or playing with toys and the player would also be able interact with the toddler itself to call other sims atention to get fed, or have his diaper changed.

Skills:

Toddlers would be able to learn one skill the "learning skill" which would rise of level when ever they lerned something new, like walking, drawing etc. after this skill got maxed when aging up children would recive a specialtrait making them level skills faster. (this would make toodler lifestage more relevant to the game and give players more of a reason to play with them)

And of course sims would have various interactions with them like cuddle, teach to..., play with, feed, change diaper etc. and objects like cribs, toys, a changing station to give them a bath or change diaper, etc.

Not realated by I also think it would be neat to have this in the game, for kids after a few days of life they should get a moodlet saying their first baby tooth got loose giving them the option to put it under their pillow with a little animation and everything and in the next day the option to see under the pillow and after the animation they should get a notification saying if they got or not a visit from the tooth fairy and if they did, they would get some simoleons.

Anyone has any other toddler ideas for the game?