Hard truth: Sims cannot carry babies or toddlers to school in The Sims 3, and no cheat unlocks this. The interaction simply doesn’t exist in the game’s code.
testingcheatsenabled true → Shift-click toddler → "Trigger Age Transition" → Child (now attends school).Sims 4 also doesn’t let you carry toddlers to school. The Parenthood pack adds a daycare rabbit hole; base game relies on nannies.