Ok original poster back again, I decided to get both a trailer and studded tyres for the bike. Both arrived and we have been using the trailer for a while now, it seems to be going great. He loves it and I find it a lot easier and safer to manage that the bike seat/carrier. Anyone out there remember that I have now tried out both options and strongly feel that the trailer is a lot lot safer and the much better option. One thing I would say is to try buy a light trailer, I did a lot of research online before I bought mine, and noticed that even some of the more expensive ones were very very heavy. The one I settled for has high headroom inside allowing for a child to wear a helmet in it and it weighs in at around 9kg.(just under 20lb I think)