ObjectiveThis study examined the association between longitudinal trajectories of lifestyle patterns (LPs) and BMI z score in early childhood.MethodsData of children (n = 439) who participated in the 18‐, 42‐, and 60‐month follow‐ups of the Melbourne InFANT Program were used. Multitrajectory modeling identified groups of children following similar LPs and BMI z score trajectories, and multinomial logistic regression assessed the determinants of the trajectory groups.ResultsThree trajectory groups of child LPs and BMI z scores were identified: “Unhealthy LP, Low BMIz” (30%), “Healthy LP, Mid BMIz” (53%), and “Unhealthy LP, High BMIz” (17%). Relative to the “Unhealthy LP, Low BMIz” group, the maternal “Fruit and vegetables” dietary pattern was associated with higher odds (odds ratio [OR] 1.22, 95% CI: 1.01‐1.47) of children following the “Healthy LP, Mid BMIz” group. Maternal prepregnancy BMI (≥25 kg/m²) (OR 2.50, 95% CI: 1.31‐4.75) and maternal TV‐viewing time ≥130 min/d (OR 2.55, 95% CI: 1.13, 5.72) increased the odds of children following the “Unhealthy LP, High BMIz” group. Child sex, breastfeeding duration, and maternal physical activity were not associated with the identified trajectory groups.ConclusionsThree trajectory groups of LPs and BMI z scores in early childhood were revealed, with maternal prepregnancy BMI, dietary pattern, and TV‐viewing time being identified as significant determinants.