Luckily it worked out for the other driver in that case. My personal injury lawyer, recently relayed a story of a client who "lightly clipped" a pedestrian. At the time the pedestrian stated he was fine and they both left without filing a report. 18 months later their client, (they are acting for the driver's insurer, in this case), is served with a lawsuit claiming damages and with supporting medical documentation for a very high six figure amount. The claim is when the pedestrian went down they struck their head and only felt the effects days later.
But regardless, in this instance the child was "hit" the media reports don't say how hard etc. The rider has a legal obligation to stop and identify themselves. Expalin how they were able, with helmets on assess any possible injury to the child? Even if the child only had a "scraped elbow or knee" that is an injury and under the HTA ALL personal injury collisions MUST be reported to police. So that is why a report is required.
There can be many reasons the rider didn't stop, (drinking, high, no insurance, warrants, previous convictions, just young and stupid/scared, etc etc etc). But they have now turned what may have been a VERY minor incident into something that they will pay for for years, (increased insurance etc).