My little one didn't grow a cm for over two years!! I was concerned - but since she had made progress, and 2cm in less than 6 months... It will happen, all in the right time. Don't worry your heart over it - just love them and they will grow!! (I'm sure already you do!)
My friend had all relatively small children, once they hit puberty they all grew very well and are now lovely and strong! - but most importantly they are confidant, happy, and well-balanced as they never cared about size or stature - just whatever The Creator chose for them... they were content.