They are all wearing normal, but classic clothing, in that lovely photo. They are the sort of clothes that parents who are sensible, and who want to buy good quality clothes for themselves and their children, will buy. These type of parents want to dress their children in clothes that can withstand being worn to climb quite a few trees, or den making, or rolling down hills in, ones that it is worth sewing buttons back on to, or darning the odd rip from when their child ended up in a prickly bush.
They are also the sort of clothes that are so well made that they can be passed onto siblings. There is nothing about the Wales' clothes that shout "look at me", or that could cause anyone seeing them to feel uncomfortable, or even embarrased. I don't think that wearing ripped jeans, T shirts with rude slogans on, trousers/jeans that show half of your bum when you bend forward, nylon, and ill fitting clothes, is necessarily something to boast about.
Unfortunately, when I had a young family (many, many, moons ago) a lot of their clothes came from supermarkets, which was because we couldn't afford anything else. Although I did always insist on Clarks shoes, or similar ones, ones that you needed to be properly measured for. I also always tried to get at least reasonable quality winter outdoor clothes for them. I was lucky in that my Dear Mum would usually pay for the more expensive, well made clothes, for her Grandchildren. So @Aquarius1234, I don't think that their clothes are at all old fashioned, they are just not items of clothing that are made to the standards of the lowest common denominator...