The Functional Independence Measure for Children (WeeFIM) was developed based on the FIMSM instrument to assess disability in children aged six months to seven years. Its reliability and validity have been studied, and normative data are available for American children. The WeeFIM instrument is potentially an internationally useful instrument, but data from other countries are lacking. The objectives of this study are to examine whether the WeeFIM instrument is applicable to Japanese children and to describe preliminary normative data. To study interrater reliability, we had two examiners assess 20 nondisabled children and calculated weighted kappas for individual item scores and intraclass correlation coefficients for total scores and motor and cognitive subscores. We then assessed 110 nondisabled children ages six months to seven years to obtain normative data and compared them with the American data. In 51 of these healthy children, we compared total WeeFIM scores with developmental ages as obtained with the Tsumori test, a standardized developmental test widely used in Japan to assess its concurrent validity. The weighted kappas were greater than 0.8, and the intraclass correlation coefficients were greater than 0.98. Total scores and motor and cognitive subscores increased with age, reaching a plateau at 60 to 72 months, which is similar to the American data. There were three patterns of chronologic changes in individual item scores: items showing high correlations with age (Spearman's rho > 0.8; grooming, dressing, memory, etc.), moderate correlations (0.8 > rho > 0.7; eating, bladder, comprehension, etc.), and lower correlations (0.7 > rho > 0.6; locomotion and chair transfer). Total scores correlated significantly with developmental ages (Spearman's rho = 0.938), but there was a discrepancy between each item score and the pass-or-fail patterns of the Tsumori test. This study demonstrated the applicability of the WeeFIM instrument to Japanese children with satisfactory reliability and validity and provided preliminary normative data for future studies.