Do you need to have the parenthood expansion pack in order to have toddlers?
According to EA, no, you do not need to have any DLC to have toddlers.
Today is a big day for The Sims™ 4. We're excited to announce the biggest update for The Sims 4 to date, and it comes in a surprisingly “little” package. Toddlers* are available as a free update for you to download into your game right now!
*Requires The Sims 4 game (sold separately) and all game updates to play.
As long as you own the base game and have updated it to the latest version, you will be able to have toddlers.