Thank you for your question. The reality is that scars are notoriously challenging to "influence" - they will usually take their own course and all you can do is try to perform damage control. Fortunately though your son is young, so his scar will more easily allow itself to be helped along.
To this regard there are a couple of pointers you should keep in mind that decrease his systemic levels of inflammatory markers, be they from the scar process itself or from something completely different like a blocked nose - they all share similar inflammatory signalling and so one can influence the other. Ensure he is cutting out as many inflammatory foods as possible - sugar, dairy, gluten, preservatives, artificial colourants and sweeteners. Secondly add in a good probiotic, usually an adult one from the fridge section of your local health shop. Probiotics not only help bowel health but keep the skin microenvironment in good running order. Thirdly introduce him to a paediatric omega 3 supplement - there are some available in liquid format and a teaspoon of this once a day will increase the availability of omega 3 in his body which can then be used as the preferred building blocks of new cell membranes instead of other "second-grade" materials that lead to anunsightly scar. Fourthly massage into the scar a good organic natural essential oil. Bio Oil is petrochemical based (horror!) and I would not advise anyone to continue applying refined petrol to their faces. Start off with a base of rosehip (3 drops in the palm of your hand) and add to it some lavender (1 drop), some marigold (1 drop) or some geranium (1 drop). Mix together and massage into his skin twice daily for as lon as it takes for the scar to whiten or to contract. Usually this can take a couple of months.
The fact that the incident occured in January will make it more challenging to alter the scar now but if you combine the systemic tips and the topical oil application then you will be hitting it in both directions with the best nature has to offer.
Best of luck, many thanks and warm regards