Abdolutely go for proper outdoor shop waterproof s as soon as they fit. You get way more for your money.
My DDs have Regatta isotex breatherble jackets about to enter their third year of being thrown in cars, rucksacks and in DD1s case draged up swiss mountains and they still look fine.
Im sure they came from go outdoors, but the kids stuff on the web isn't as good as the shop.
Also Gloucester quays outlet mall has mountain life and other outdoor suppliers who have childrens sizes with very good discounts, so I guess other similar places might.
Well worth a trip as waterproofs all feel and fit differently and DC sleeve lenths are crazy.