It was in Dublin a few years ago '11 or '12, I think. To me it seemed to be like there was an age threshold at which people start to wear regular clothes.

To say something nice: People were extraordinary friendly and walked up to us from 20-30m (100 feet) away to help us when we looked even remotely disoriented :)

Well, it makes sense that it'd be Dublin. More than likely you were seeing people who live in more deprived parts of the city. I can't say I've seen many children around Dublin dressed like that, mainly teenagers and younger adults.

I hope you'd a good time while you were here! I recommend you see some other parts of the country. For instance, Cork and Galway are great cities.