The portrayal of diet over time is a natural progression from the characterization of diet at single time points. The transition dietary period, a dynamic period of rapid dietary change spanning infancy and toddlerhood when children shift from a milk-based to a food-based diet, has not been characterized.The objective was to summarize variation in dietary intakes spanning infancy and toddlerhood.A prospective principal components analysis was applied to dietary intakes from 3 successive follow-ups of children enrolled in the ALSPAC (Avon Longitudinal Study of Parents and Children). The frequency of food and beverage consumption was assessed via questionnaire at ages 6, 15, and 24 mo (n = 2169).Two types of transition diet were identified. The first transition diet was characterized by the consumption of home-prepared and raw foods ("healthy") at all time points and the second by ready-prepared and discretionary foods ("less healthy") consistently over time. Higher educational level and maternal age were associated with higher scores on the "healthy" diet, whereas younger maternal age and a lower educational level were associated with higher scores on the "less healthy" diet. Maternal BMI, number of older siblings, and lower social class were associated with the less-healthy transition diet but not with the healthy transition diet.Unique transition diets, including a less-healthy type, emerge by age 2 y. These diets are consistent with childhood and adult dietary patterns reported at single time points and show convergent validity both with known maternal sociodemographic predictors of childhood diet and with intake gradients across diet scores.