Early-life exposure to tobacco is associated with obesity, but the most susceptible developmental periods are unknown. To explore windows of susceptibility in a cohort of 568 mother-child pairs. We measured seven measures of tobacco exposure (five self-reported and two biomarkers) spanning from pre-conception to age 5 years. Mothers self-reported active smoking (pre-conception, 17 weeks, and delivery) and household smokers (5 and 18 months postnatally). Cotinine was measured in maternal urine (27 weeks) and child urine (5 years). Adiposity (fat mass percentage) was measured at birth and 5 years via air displacement plethysmography. Using a multiple informant approach, we tested whether adiposity (5 years) and changes in adiposity (from birth to 5 years) differed by the seven measures of tobacco exposure. The associations may depend on timing. For example, only pre-conception (β = 3.1%; 95% CI: 1.0-5.1) and late gestation (β = 4.0%; 95% CI: 0.4-7.6) exposures influenced adiposity accretion from birth to 5 years (p for interaction = 0.01). Early infancy exposure was also associated with 1.7% higher adiposity at 5 years (95% CI: 0.1-3.2). Mid-pregnancy and early childhood exposures did not influence adiposity. Pre-conception, late gestation, and early infancy exposures to tobacco may have the greatest impact on childhood adiposity.