Dear Physio. The particular case is of Orthopedic concern, all the problems of this child like Lordosis, Flatfooted etc. are secondary to B/L Coxavalga ie compensatory mechanism as the flatfoot and loss of roll over of foot is due to abducted legs to compensate the profound waddling gait, Lordosis is to make center of gravity between the feet during walking. He must have deformity little more on right side as u described the condition.
The actual need is wedge osteotmy to treat valgus deformity. As much as Physio's. Concern Stretching is helpful, strengthening of Abdominals, Invertors of feet, and Adductors, Extensors of hip. U can incorporate a medial wedge as medial arch to feet in the shoes. Concentrate on the walking pattern to improve.