It does sound edwardian, bearing in mind that having a photo taken was a luxury to most people, there is usually a life event that prompted it. I don't think it was very common for children to be photographed individually either. It could well be that there was a family wedding at the time though and he was dressed up for that, certainly the sailer suit was the Sunday Best outfit in a middle class family.
This site is very detailed but you will need the info from the reverse of the photo.
http://www.cartes.freeuk.com/time/date.htm
The key info is the phtographers address on the reverse as this links it to a particular line in your tree,.