In our family the DDs buy the school shoes and out of school shoes, simply because they can easily take the children to the shop for fitting. However we always buy other items, trousers, shirts, pinafores etc. having checked their sizes with the DDs.
Several years ago our County Education Authority, standardised uniform through out the County Schools (Primary & Secondary) to Black Blazers, black shoes, white shirts/blouses and black or grey skirts/trousers. Each school then has its own tie, badge and individual colours for Polo shirts. This makes buying and reusing uniform easier on parents if the pupils change schools and permits handing down uniforms to siblings, cousins and friends even if they are at different local schools. It is a totally brilliant idea - good recycling, saves parents money, means that standard items can be bought in M & S or any supermarket, even Aldi or Lidl. No specialist uniform shops with inflated prices, badges, ties etc. are ordered via the school at bulk prices.
It also allows one of our Food Banks, with help from our local MSP, former MP and WFI Group to operate a School Clothing Exchange, where parents can swap out-grown, good condition School Clothes for larger sizes. Stock is boosted by donations of brand new items by well wishers, supermarket collections and unclaimed items left behind in each school. The standardised uniform means that clothes from any school will be suitable for any other school.