Here's my twopennyworth:
As has been said, the clothing (and, indeed, the quality of the photographic process) suggests the WW1 period, rather than WW2.
The absence of men of war service age in the photograph suggests that the photo might show celebrations to mark the end of WW1.
I'm surprised that Dave sees the tricolour as either Belgian or Irish, as the central band appears to be white (rather than yellow), thus ruling out the Belgian flag, and the contrast ratios of the outer two bands seem to be inconsistent with the green and orange of the Irish flag (which would look very similar in monochrome). My guess is that it's the French tricolour.
Identifying the flags might not help much anyway. It's quite likely that somebody just grabbed all of the flags and bunting that they could lay their hands on and flew the lot, possibly without even knowing which nations were represented by them.
Even so, the absence of both the flags of St David and of Wales does seem to be a little odd.
While it's possible that the 'RE' flags make up part of 'remember' (as Horseshoes has suggested), or even possibly 'rejoice', I feel that it's more likely that the letters 'R E' are simply the initials of a local or national organisation which was helping people through the war. (The name of such an organisation might well be in Welsh, of course).