Unused cycling overshoes - Shimano size 6-7 (UK)

I bought these Shimano cycling overshoes for my 12 year old son in Decathlon last week for €32 and stupidly took the tags off before getting him to try them on. They're too small so I'm selling them as new but with no tags for half what I paid. The tag said size 6-7 and the label sewn in says "M". To be honest, they fit more like a size 5-6 (UK) I'd say. Happy to post anywhere in Ireland.