Hip joint reconstruction is often necessary for children and adolescents with conditions like developmental dysplasia of the hip (DDH), neurogenic dislocation of the hip (NDH), or Legg–Calvé–Perthes disease (LCPD) when non-surgical treatments are ineffective. Background: Post-operative immobilization after hip reconstruction in children is crucial to promote proper healing and reduce the risk of complications. While spica casting has been the traditional method, it can lead to various issues. Foam splinting has emerged as an alternative approach. This study aimed to compare the effectiveness and satisfaction of the patient and the caregivers of spica casting and foam splinting after pelvic osteotomies in young patients with DDH, NDH, and LCPD. Methods: A prospective randomized clinical trial included patients aged 3 to 16 undergoing pelvic reconstruction (iliac and proximal femoral osteotomy, open reduction, and soft tissue procedures). Participants were randomized into two groups: one receiving spica casts and the other foam splints, both for a six-week period post-surgery. Quality of life (QOL) assessments like CPCHILD, SF-36, and EQ-5D were conducted using various scores to measure patient and caregiver satisfaction preoperative and at six and twelve weeks postoperative. The surgical techniques were consistent across both groups. Results: The study included 34 patients, with one excluded due to non-adherence. The spica cast group experienced statistically significant declines in QOL scores, while the foam splint group showed decreases that were not statistically significant. Complications were reported in 11 patients, with a higher prevalence in the spica cast group. Conclusions: The foam splint group demonstrated superior satisfaction levels and fewer complications, which leads to the conclusion that foam splinting should be the preferred option to spica casting for post-operative immobilization in these cases.