I spend all my youth in the north of France. I have never heard of the behavior you describe. AFAIK, the rules are rather well applied and children are well informed to avoid accidents.
Children, totally - I lived in Alsace for about six months as a kid, and was repeatedly warned not to touch any weird looking objects in woods, fields, etc., not that it stopped me from ferreting around in old bunkers.
I've never seen it done, but I did meet a farmer with an impressive array of ordnance stacked in his grange, some of which he sold, the rest of which he said he burned in a deep hole. Sure, single data point, but he definitely held the "this is what we do" attitude. This would've been '93.
