Distinguishing physiologic and pathologic genu varus is challenging among children below age 3. They can be assessed by measuring intercondylar distance (ICD), clinical tibiofemoral angle (cTFA) or radiologic TFA (rTFA). We aim to determine the knee measurement values among three groups of children. Medline (1946-) and EMBase (1947-) were searched until 31 July 2020 using a search strategy. Studies with original data which reported knee measurements among children with normal alignment, physiologic and pathologic bowing between the ages of 0-3 years were included. In total 1897 studies were identified, and 16 studies included after title and abstract screening. These studies involved 1335 patients with normal alignment, 286 with physiologic and 184 with pathologic bowing. Five studies provided data on ICD, seven on cTFA and eight on rTFA which were pooled for meta-analyses. Normal children had neither measurable ICD nor demonstrable varus on cTFA after 19 months old. The mean (95% confidence interval) ICD for children with pathologic genu varus at 18 months was 4.41 (4.19-4.63). The rTFA for children with pathologic compared to the physiologic bowing by age groups was; 11-20 months: 24.74°(23.22°-26.26°) vs. 19.44°(17.05°-21.84°), 21-30 months: 20.35°(18.13°-22.56°) vs. 14.72°(12.32°-17.12°) and 12-36 months: 32.60°(26.40°-38.80°) vs. 19.14°(17.78°-20.50°). Children above the age of 18 months with genu varus should be closely monitored clinically using ICD or cTFA. An ICD of more than 4 cm may warrant further investigation for pathologic cause. rTFA has limited use in the detection of pathologic varus.