In Norway’s chic capital, Oslo, and the pastel-hued second city, Bergen, my family and I found the summer climate to be perfect. T-shirt and shorts weather, but it was never too steamy to trek a mountain trail, stroll Bryggen’s medieval wharf, or cruise the fjords. For our three children (aged 10, eight, and five), the two cities felt like one enormous playground — not least because Norway has trains with entire carriages devoted to soft play.