Unlike teens, adults or elders, children can't interact with toddlers in many ways. If they have not been potty trained, they also depend on older Sims to either change their diapers or take them to the potty when necessary. They depend on older Sims ( teens, adults, or elders) to feed them, put them into and take them out of their cribs, carry them up and down stairs, and bathe them.
Toddlers require the most attention of any life stage given their lack of independence. Its personality and interests are visible, and it is controllable.
When a baby turns into a toddler, most of its genetic traits become visible for the first time. The manual suggests this isn't possible, but it actually is. All toddlers have the Grow Up aspiration and can start earning aspiration points, although they won't be able to redeem them until they are teens, unless the FreeTime expansion pack is installed.
It is the youngest life stage that can be created in Create-A-Sim. Toddler is the second life stage in The Sims 2, and it lasts for four days.