This paper presents an innovative design methodology for development of lower limb exoskeletons with the fabrication and experimental evaluation of prototype hardware. The proposed design approach is specifically conceived to be suitable for the pediatric population and uses additive manufacturing and a model parameterized in terms of subject anthropometrics to give a person-specific custom fit. The methodology is applied to create computer-aided design models using average anthropometrics of children 6-11 years old and using anthropometrics of an individual measured by the researchers. This demonstrates that the approach can scale to subject weight and height. A prototype exoskeleton is fabricated, which can actuate the hip and knee joints without restricting hip abduction-adduction motion. In order to test usability of the device and evaluate walking assistance, user effort is quantified in an assisted condition where the subject walks on a level treadmill with the exoskeleton powered. This is compared to an unassisted condition with the exoskeleton unpowered and a baseline condition with the subject not wearing the exoskeleton. Comparing assisted to baseline conditions, torque magnitudes increased at the hip and knee, mechanical energy generated increased at the hip but decreased at the knee, and muscle activations increased in the Vastus Lateralis but decreased in the Biceps Femoris. While the preliminary evidence for walking assistance is not entirely convincing for the tested conditions, the presented design methodology itself is promising as it has been successfully validated through the creation of computer-aided design models for children and fabrication of a serviceable exoskeleton prototype.