This condition may occur due to weakness of bones. It's called Genu varum.
For at, you need to get one x ray of whole lower limbs called Scanogram to identify the bony deformity.
Next Steps
Depending on the severity of the condition as per x ray, treatment may he planned. Surgery is required in cases of severe deformity. Physiotherapy and some braces are also available in cases of minimal deformity..