A longitudinal study of almost 9,500 children identified two patterns of BMI changes: 1) a decrease until age 6 and an increase until age 9 in 89% of the children, and 2) an increase from age 3.5 to 9, reaching a mean BMI at age 9 that was over the 99th percentile in 11% of the children. The atypical group was more strongly associated with maternal smoking and high BMI.
Summary: https://medicalxpress.com/news/2025-06-distinct-childhood-bmi-patterns-prenatal.html
Original paper: https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2834361