I don't know if you can see it, but for me there is already melancholy and death in the above picture - it is a natural by-product of certain photographs. I'm not dissing it, in fact I'm positively seeking it out, even at 21st birthday parties: it's life baby, part of the Rich Tapestry one hears so much about. Why is it present in the above? I think because the ephemeral nature of the balloons combined with their obviousness and their lurid, look-at-me presence, plays so well against a celebration of a milestone: maybe this is my old head playing tricks on me, but a photo like the one above already has melancholy at its heart because we remember what life promised and then how it turned out.
On the other hand, maybe it is simply yearning for times past.