Children with cerebral palsy (CP), have impaired postnatal muscle growth, with some muscles developing contractures. Functionally, children are either able to walk or primarily use wheelchairs. Satellite cells are muscle stem cells (MuSC) required for postnatal development and source of myonuclei. Only MuSC abundance has been previously reported in contractured muscles, with myogenic characteristics assessed only in vitro. We investigated if MuSC myogenic, myonuclear and myofiber characteristics in situ differs between contractured and non-contractured muscles, across functional levels, and compared to typically developing (TD) children with musculoskeletal injury. Open muscle biopsies were obtained from thirty-six children (30 CP, 6 TD) during surgery; contracture correction for adductors or gastrocnemius, or from vastus lateralis (bony surgery in CP, ACL repair in TD). Muscle cross-sections were immunohistochemically labeled for MuSC abundance, activation, proliferation, nuclei, myofiber borders, type-1 fibers, collagen content in serial sections. Although, MuSC abundance was greater in contractured muscles, primarily in type-1 fibers, their myogenic characteristics (activation, proliferation) were lower compared to non-contractured muscles. Overall, MuSC abundance, activation and proliferation appear to be associated with collagen content. Myonuclear number was similar between all muscles, but only in contractured muscles were there associations between myonuclear number, MuSC abundance and fiber cross-sectional area. Puzzlingly, MuSC characteristics were similar between ambulatory and non-ambulatory children. Non-contractured muscles in children with CP had a lower MuSC abundance compared to TD-ACL injured children, but similar myogenic characteristics. Contractured muscles may have an altered developmental progression of postnatal MuSC pool establishment, needed for lifelong efficient growth and repair.