Lower limb orthoses are frequently used in children suffering from cerebral palsy (CP) alongside rehabilitation. The aim of this study was to analyze the effectiveness of ankle-foot orthosis (AFO) and knee-ankle-foot orthosis (KAFO) in walking, balance maintenance, spasticity, and quality of life improvement during rehabilitation in children affected by CP. The hypothesis was that the use of orthoses could improve the parameters compared to non-use. A systematic review was conducted in the main databases, including English language RCTs published about the use of AFO and KAFO in combination or not with rehabilitation methods in children affected by CP and studies mentioning walking, balance, muscle length, and quality of life as outcomes. From an initial number of 1484 results, a final number of 11 RCTs were included, comprising a total number of 442 participants and showing an overall high risk of bias in 10 studies and some concerns in one study. Six studies investigated the domain of walking, four studies investigated the domain of balance, and two studies investigated how KAFO and AFO orthoses could improve and prevent muscle contractures. Using highly heterogeneous study designs, different kinds of orthoses and different assessment tools were used. Further studies conducted with higher methodological quality are needed to establish whether AFO and KAFO are useful or not in combination with rehabilitation in improving the investigated domains.