This study reports on a novel methodology using the V-scope to quantify elbow and shoulder movement in young children with obstetric brachial plexus palsy (OBPP), and the intra- and interreliability of this method. The V-scope, a portable, inexpensive movement analysis system, was configured in an L-shape, with two transmitting towers placed on the floor and one 1.35m off the ground. These towers received ultrasonic pulses from buttons that were placed over standardized landmarks of the child's trunk, chest, and upper limb. Two physiotherapists (a paediatric and a generalist) facilitated the maximum range of active elbow flexion/extension and shoulder abduction/flexion in 30 children with OBPP (18 females, 12 males; age range 6mo–4y 7mo; mean age 2y 6mo [SD 1y 2mo]). Assessments were conducted on two occasions, one week apart. The V-scope was found to be feasible to use by a specialist and a generalist physiotherapist, demonstrating moderate to high reliability coefficients, small measurement errors, and lack of missing data. The pediatric physiotherapist was more reliable in measuring elbow and shoulder movement compared with the generalist physiotherapist, which suggests that the same experienced, pediatric physiotherapist should assess elbow and shoulder movement across all occasions of testing.