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Maturational differences exist in cardiopulmonary and cerebrovascular function at sea‐level, but the impact of maturation on acclimatization responses to high altitude is unknown. Ten children (9.8 ± 2.5 years) and 10 adults (34.7 ± 7.1 years) were assessed at sea‐level (BL), 3000 m and twice over 4 days at 3800 m (B1, B4). Measurements included minute ventilation (V̇E${\dot{V}}_{\rm{E}}$), end‐tidal partial pressures of oxygen (PETO2${P}_{{\rm{ETO}}_{\rm{2}}}$) and carbon dioxide, echocardiographic assessment of pulmonary artery systolic pressure (PASP) and stroke volume (SV) and ultrasound assessment of blood flow through the internal carotid and vertebral arteries was performed to calculate global cerebral blood flow (gCBF). At 3000 m, V̇E${\dot{V}}_{\rm{E}}$ was increased from BL by 19.6 ± 19.1% (P = 0.031) in children, but not in adults (P = 0.835); SV was reduced in children (−11 ± 13%, P = 0.020) but not adults (P = 0.827), which was compensated for by a larger increase in heart rate in children (+26 beats min−1vs. +13 beats min−1, P = 0.019). Between B1 and B4, adults increased V̇E${\dot{V}}_{\rm{E}}$ by 38.5 ± 34.7% (P = 0.006), while V̇E${\dot{V}}_{\rm{E}}$ did not increase further in children. The rise in PASP was not different between groups; however, ∆PASP from BL was related to ∆PETO2${P}_{{\rm{ETO}}_{\rm{2}}}$ in adults (R2 = 0.288, P = 0.022), but not children. At BL, gCBF was 43% higher in children than adults (P = 0.017), and this difference was maintained at high altitude, with a similar pattern and magnitude of change in gCBF between groups (P = 0.845). Despite V̇E${\dot{V}}_{\rm{E}}$ increasing in children but not adults at a lower altitude, the pulmonary vascular and cerebrovascular responses to prolonged hypoxia are similar between children and adults. Key points: Children have different ventilatory and metabolic requirements from adults, which may present differently in the pulmonary and cerebral vasculature upon ascent to high altitude.Children (ages 7–14) and adults (ages 23–44) were brought from sea level to high altitude (3000 to 3800 m) and changes in ventilation, pulmonary artery systolic pressure (PASP) and cerebral blood flow (CBF) were assessed over 1 week.Significant increases in ventilation and decreases in left ventricle stroke volume were observed at a lower altitude in children than adults.PASP and CBF increased by a similar relative amount between children and adults at 3800 m.These results help us better understand age‐related differences in compensatory responses to prolonged hypoxia in children, despite similar changes in pulmonary artery pressure and CBF between children and adults. [ABSTRACT FROM AUTHOR]