Background and Objective: Existing evidence in the association between maternal pregnancy and pre-pregnancy weight and behavioural outcomes in children is limited and inconsistent. This study aimed to examine these associations at five developmental time points between ages 3 and 16. Methods: We used data from the Avon Longitudinal Study of Parents and Children (ALSPAC), an ongoing population-based longitudinal pregnancy cohort study in Bristol, United Kingdom (UK). Data on behavioural outcomes were measured at ages 3.5, 7, 9, 11 and 16 years using the Strengths and Difficulties Questionnaire (SDQ). Over 7960 (at 3.5 years of age) and 4400 (at 16 years of age) mother-child pairs were included in the final analysis. Generalised estimated Equation (GEE) and logistic regression analyses were used to examine the associations. Results: Preconception underweight was associated with emotional symptoms in children (OR = 1.38, 95% CI; 1.15 – 1.66). We found an increased risk of peer relationship problems in the offspring of mothers with pre-conception overweight (OR = 1.17, 95% CI; 1.01 – 1.35) and obesity (OR = 1.41, 95% CI; 1.13 – 1.74). Preconception BMI was not associated with hyperactivity/inattention problems and conduct problems. We also found no evidence of the association between gestational weight gain and child behaviour.   Conclusions: Our Findings highlight that preconception BMI, but not gestational weight gain, may influence the emotional health of children and adolescents.