Can only echo what a lot of the others have said. I have a 5 year old who's extremely tall for her age, so at the age of 3 some of her stuff was already age 5 to 6, and now, a lot of it is age 7 to 8.
I wouldn't say it's impossible to dress her appropriately, but it's certainly not easy either. H&M have so far proved to be very good value but she's right on the cusp now between their "little" girl range and their "older" girl range, a lot of which looks very sombre (dark and gothic) and some of which I'd define as tarty. Indisputably, amongst the supermarket ranges, there's a lot of clothing for "older" girls, eg. from 6 plus, which is sombre, sparkly, and verging on "sexy" (I appreciate that's a subjective term, but a lot of you'll know what I mean) ...... very short skirts, backless tops, dodgy slogans and so on. I wouldn't claim that it's all like that but I despair at the "choice" offered.
I agree John Lewis usually has lovely girls' clothes .... which my daughter loves too, but there's no way I can afford £40 for an (admittedly very pretty and well made) pinafore dress when I'd think twice about spending the same on myself (and I'm not going to grow out of it). Similarly, Boden is out of the question financially and though Next isn't quite as expensive (and does have some very odd stuff sometimes) their prices are still on the high side of what I really want to pay.
I guess the buyers for "cheaper" stores would argue there's a market for the trashy/tarty stuff ....... they may as well say that if you're not especially well off (or indeed simply and sensibly don't want to spend a lot of money on clothes which will get comparatively little wear) it's okay for them to view your children as potential jailbait. I guess I find it really offensive to be offerred inappropriate stuff in the 1st place ....... okay I don't have to buy it, but is that how they see their customers ??