How to Prevent Scarring from Wound on a Baby?

My little girl fell against the edge of a cupboard at a nursery causing a large hematoma about 1cm on her forehead with a shallow vertical cut in from the edge. The cut was not stitched or glued due to the delay getting treatment (3hrs-it-had-fully-clotted). 5 days later, the scab has fallen away leaving at this stage a visible gap in the surface around 1mm wide.There is still significant bruising and some swelling. What would be the best way to mitigate any scaring? The attached picture was taken 4 days after the accident. Any advice/reassurance would be greatly appreciated.