Do you need the base game for De Sims 4: Samen Groeien?
Yes. De Sims 4: Samen Groeien is extra content and only works if De Sims 4 is already on the same account and the same platform. Without the base game you can redeem the code but play nothing.
Same account, same platform
Buy the DLC for the platform where you already own De Sims 4. Redeeming it on another account or console makes the content unusable, and that cannot be reversed.