The best piece of advice I ever had on keeping kids fit at home was from Joe Wicks, the guru of these things: start them young. There are things you can persuade a four-year-old to do with a sticker that, by the time they are six, would be more like a quid; if you wanted to bribe a 12-year-old to do a daily plank, from a baseline of no-daily-plank, that would cost you roughly £1m. Unfortunately, to really make use of this excellent advice, I would have to go back to 2013. I have two 12-year-olds and one 10-year-old. The older two are less biddable, but each has a sport (C has karate, TJ has tennis and cycling) and some semblance of a sport ethic to go with it. The youngest has nothing of the sort. We used to call her H the Quitter, and don’t write in to explain why that is wrong because we knew it was wrong at the time. To concentrate on the big ones: stick to their sport and make it their thing. Even the most rebellious soul cannot help forming habits; if there is any livestreamed...