Background <p>Hypertension has recently shown a rapid rise in prevalence among children and adolescents. It can track into adulthood and tend to manifest at an earlier age. It should be prevented urgently and efficiently.</p> Methods <p>This study assesses the prevalence of occasional hypertension (OHTN) at 5 ~ 6 years old and evaluates its association with size at birth and BMI at 2 and 5 ~ 6 years old in full-term children. We conducted a population-based cohort study of 12,564 children from 66 kindergartens in Tianjin, China. Information on birth weight, body mass index (BMI) at 2 and 5 ~ 6 years old, and blood pressure at 5 ~ 6 years old was retrospectively collected.</p> Results <p>The prevalence of childhood OHTN (SBP or DBP ≥ P₉₅ percentile for sex, age, and height) was 17.0%. At birth, SGA has a high risk of OHTN (AOR 1.36, 95%CI 1.10–1.68). In the SGA subgroup, although children are of normal weight at 5 ~ 6 years old, excessive catch-up growth (BMI ≥75th at 2 years old) was still attributed to OHTN (OR 1.51, 95%CI 1.03–2.24). Obesity (BMI ≥2SD at 5 ~ 6 years old) was a vital risk factor for OHTN (AOR 2.93, 95%CI 2.56–3.36) unregarding with birthweight (OR 95%CI: SGA 3.23(1.66 ~ 6.27), AGA 2.83 (2.42–3.31), LGA 3.52 (2.65–4.68)). The co-presence of moderate or excessive catch-up growth before 2 years old and obesity at 5 ~ 6 years old significantly increased the risk of childhood OHTN (OR from 2.74 (1.65–4.54) to 6.53 (2.68–15.90)).</p> Conclusions <p>Preschool obesity, low birth weight, and excessive catch-up growth increased the risk of OHTN in childhood.</p>