"flowery- can you say what you think might happen?"
There are some unpleasant people out there. Many times I've had to deal with (by which I mean ignore, and not be worried by) drunk people, intimidating people, groups of people behaving badly on trains. A rowdy group of sports fans can feel intimidating, for example.
Of course not all the time, and usually it's fine, but I sometimes feel vulnerable, and I wouldn't be happy putting two young boys (in my case) in that position where I couldn't easily go and get them.
I'm also conscious that DS1 who is 12, actually looks about 8, and is the same height as my 9yo, and that would influence me as well.
If he's had a growth spurt by a year's time my view might change, but he seems (and is) very little at the moment, and also takes the weight of the world on his shoulders, (unlike DS2!) and would worry.