Certainly on road cycling in a British city can be "challenging" - I used to have a 10 mile cycle commute through the center of Edinburgh for a few years and I had a number of incidents that were pretty scary.

However, things are getting better - Edinburgh has a pretty decent cycle path network (mostly on old railway lines, so they sometimes appear to be ridiculously over-engineered - with huge bridges and tunnels). We had a family cycle on Sunday morning where we cycled for about 3 hours with perhaps 15 minutes of that being on roads.

I wouldn't let kids cycle on roads by themselves though - something I did as a child from an early age without thinking about the dangers (I did grow up in a small village in the north of Scotland!).