just putting this out there for anyone that doesn't know.
my sons left joy con has had drifting issues for a long time, we just assumed that he had done something to cause it, whilst looking for switch deals I come across an article which explains how this is a common fault! and that nintendo will either fix the Joy-Con or replace it if it can't be fixed free of charge, as long as you have proof of purchase. so after going on a mad one searching for the receipt and apologising to my son, we will now be getting the problem fixed!!
again, just putting this out there for anyone that has the same issue and didn't know !!