I'll second the Land's End suggestion. My kids' school uniforms come from Land's End - Kids. They have a decent collection of trad/prep/whatever style clothing at prices that won't break the bank. If you sign up for their e-mails you'll get discount offers from time to time.
Ralph Lauren has terrific, well-made kids clothes, and it's quite a deal during their sales seasons. Hanna Anderson as well (I have a daughter - if there isn't a "boy version" of Hanna Anderson, there should be!)
A challenge I've had lately for my daughter (6), at least buying clothes in the USA, is that the things which fit her in length (and she is *tall*, about 49" which puts her in the top percentile for her age) are too baggy... because the clothing makers are catering to the (increasingly common) fat kids!
My daughter is *extremely* active (I may have a future jock - or whatever the term is for a girl jock - on my hands!), and in spite of eating like a horse is rail-thin (as 6 year olds should be), but already other kids her age are starting to show signs of pudge. They're throwing off the marketplace!
We spend a lot of time in Japan, and buy clothes there (which are much more fitted), but excepting Uniqlo, Japanese kids clothes are pretty premium (like $150 for a nice dress).
I find Ralph Lauren has a better fit, a little more fitted or tailored, so to speak.
(It matters because kids should wear pretty form-fitting clothes, so as to facilitate crawling through brush and leaping from rocks and generally being a woodland ninja).
The choice of clothing & how much to spend on it typically depends on factors like household income, kids age, etc. Amazon, Ebay, Olesia are the best option to buy children’s dress online. Here you will get quality & trendy clothes for your kids.