S.E.
There is Once Upon a Child in De. It's right on Rt 7 in the same shopping center as KMart. The clothes are usually in good condition and the prices are generally reasonable.
The other one is don't overlook Goodwill. Many people turn up their noses at it, but for kids clothes its great. You just have to be selective and careful, but who can beat the prices? The one on Kirkwood hwy seems to have pretty good stuff.
(Actually for grown up clothes sometimes you can get really lucky there too. I got a pair of brand new Feragamo shoes last year, still in the box, for $5!)