Hi -
As a Teaching Assistant I taught recorder in primary school for ten years; also informal keyboard club with Year 6, and percussion with Yrs 1 and 2. The percussion kids accompanied the school Christmas production each year.
Music is certainly one of the most satisfying skills that a person - child or adult - can learn, and can give life-long pleasure. I admire all the support you are giving DS, and the different activities that he now feels confident enough to tackle. But do take care that he doesn't try to do TOO much, or he may get overtired, and sometimes he may feel he needs a rest from some activity for a week or two. If that does happen, try not to 'pressure' him, or he may get discouraged.
I don't know if you realise it, but the violin is one of the HARDEST instruments to learn, and progress will be very slow at first, so it could be several months before he starts to play anything like a real tune.
However, do you, as a family, have access to a piano, or an electronic keyboard? If you do, DS and you could start learning little things that could make simple tunes, while he is still learning to use the bow, and keep on the correct string on the violin. Or recorder might be another possibility, and certainly the cheapest. I started recorder children in Yr2, as younger than that it is possible their fingers are too small to cover the holes.
I will 'keep an eye' on this thread, and see if I can be of any more help.
Did you see any of the Classic Brit Awards on ITV recently? Try and have a look at Nicola Benedetti with Lang Lang (the first item in the programme.) She was winner of the BBC Young Musician of the Year ten years ago, and is one of the UKs most succesful violinists now.