Not long ago Piazza Navona used to be the playground for centre-city kids. In the mornings it would be full of mothers and babies in pushchairs (plus grandmothers and English au-pairs); in the afternoon it was full of school-age children riding their bikes or kicking footballs. There was a bike rental shop, which has now become a restaurant; there was a little slope in front of the Brazilian embassy which was good for a fast downhill pedal into the square, made even more daring because the embassy