Pippa Middleton wrote about trying alternative therapies for her son, Arthur, in her new Waitrose Weekend column. Our local baby gym has been a saving grace. "I needed to find something more than just park walks in the pram," wrote Kate Middleton's younger sister about staying active with her young son“Starting my son Arthur swimming at four months old has given him confidence and enjoyment in water,” she wrote. Arthur has been seeing an osteopath since he was seven months old. It’s a big space full of fun, soft objects, play mats, stairs, balls, swings, mini trampolines and more to stimulate and physically engage babies and toddlers.”Pippa added that swimming is fun for both mother and son: “Water activity is a great form of exercise you can do with your baby.” 'Shorts on young boys is one of those silent British class markers that deliberately harks back to a bygone age.Kate Middleton's sister, 36, put on a casual display in jeans and trainers as she opted to dress the youngster, 19 months, in a quilted jacket and shorts for a coffee run in West LondonPart of the Daily Mail, The Mail on Sunday & Metro Media Group'British upper classes - and particularly royals - are especially keen to hold on to tradition so this sartorial one will silently mark them out from "the rest". The exercise helps guarantee sound daytime sleeps, and the movement has improved his digestion.”“Arthur burns lots of energy in this safe environment and learns many physical skills,” the mother of one said. Pippa Middleton's son Arthur was seen wearing shorts in an 'aristocratic' fashion move that echoed his cousin Prince George's wardrobe during an outing in London this week.. Kate Middleton… Pippa Middleton, sister of the Duchess of Cambridge, dressed down in jeans and a long coat to take her son, Arthur, for a birthday stroll in London. Pippa Middleton has revealed a gorgeous glimpse of her baby son Arthur during a holiday in the sun with husband James Matthews. “I have also noticed him building his confidence with each visit.”Pippa, 36, explained that in addition to free play, there are classes with “structured activities that help promote movement, balance and strength.”“Now that Arthur is 11 months old and more mobile, I have been trying to come up with different activities to do with him,” she wrote. 'Trousers on young boys is considered a tad 'suburban and middle class'.Following his tragic death, brother James Matthews accompanied by wife Pippa have become committed to fundraising for poverty-stricken areas in Africa and Asia through the Michael Matthews Foundation.Despite being seen taking his first steps without the pram over the past week, Pippa opted to keep the little boy in the pushchair as she ran errands on the busy streets of West London.Published by Associated Newspapers LtdHe went on to explain that the youngster would no doubt be following traditions from a bygone era, which most aristocratic families - and public schools - obey.Previously, MailOnline's etiquette expert William Hanson told Femail that Kate put her son exclusively in shorts as it's an aristocratic way to dress, harking back to the times of 'breeching', when boys would wear shorts until the age of 8, when they had a party to celebrate the move into trousers.This time she's teamed her distressed skinny jeans with a Sandro biker jacket and these snake print kicks, which are by Cocorose London.