English-speaking adults often recruit a “mental timeline” to represent events from left-to-right, but its developmental origins are debated. Here, we test whether preschoolers prefer linear representations of events and whether they prefer culturally-conventional directions. English-speaking adults (n = 85) and 3-to-5-year-olds (n = 513; 50% female; ~47% white, ~35% Latinx, ~18% other) were told 3-step stories and asked to choose which of two image sequences best illustrated them. We found that 3- and 4-year-olds chose ordered over unordered sequences (r 3yo = 0.29, r 4yo = 0.74), but preferences between directions did not emerge until age 5 (r 5yo = 0.37, r adult = 0.91). Together, these results show that children conceptualize time linearly early in development but gradually acquire directional preferences (e.g., for left-to-right).