The obvious answer is that the problem isn't the age or ability of the cyclist but that for parents there is not really an option to cycle safely and legally with children in large parts of the UK.
I started riding with my son on the roads four years ago when he was 9, but for the most part it was horrible. I didn't enjoy it at all, it's one of the most horrible things ever watching your precious child get close passed deliberately or impatiently.What is wrong with people? But I was passionately committed to the idea of our right to cycle so I persevered.
When I got deliberately driven into 18 months ago, I stopped taking my son out by bike. It was the straw that broke the donkey's back. I realised I wasn't prepared to risk him being injured in the same way. Now I either drive or take the bus when we go somewhere together.
Recently, we had to go to one of his football matches a few miles away that we couldn't really get to by bus (the buses here are crap, especially evenings and weekends) and I didn't have the car that day (I haven't got a car, it's my boyfriends car that I borrow occasionally) so took the very rare decision that we would ride. I checked out that there were pavements on the roads that felt too dangerous to ride on.. We were riding on a pavement, a wide one, very slowly, considerately. We stopped to allow a couple who were coming towards us to pass unhindered and were subjected to some very unpleasant ranting by the old man.
I pointed out to him that roads weren't safe for children and that we'd stopped to allow them to pass unhindered, but he just ranted more.
Safe cycle infrastructure that can be used by children is absolutely vital, until we get that, we are not going to see people give up their cars and all the benefits that come with that.