Hi I think my child is bow-legged. Is there any ways to certify that or what do I need to do about it?

Like Hui Qun mentioned, the baby will grow out of it and eventually his legs will straighten out naturally. By the time the baby is a pro a running/walking, he would grow out of it. But by 20 months old, if you still noticed the bow-legged, you can choose to bring your child to the doctor's. Here's a clinic in Singapore that you might want to consider: http://www.boneclinic.com.sg/orthopaedic-conditions/child-orthopaedics/rotational-deformities-in-children/