I'd second the MEC call. They have pretty good quality, fairly priced gear, with a pretty active environmental policy.
It might sound crazy, but the other one to watch is Patagonia. They have some smoking Web Special deals on kids stuff, that seems to last REALLY well. I picked up some $23 fleeces about 4 yrs ago, that are still doing the rounds of our neighbour hood. These things were worn to school every day, as well as being thrashed in the bush. The same with their Cap 3 thermal tops for $13. The kids are happy to wear them as long t-shirts to school. Choose bright gender-neutral colours. This means I can spot the orange discarded fleece on the other side of the playground when I pick the kids up. Black and dark blue fleeces seem to last about 2-3 weeks before they get 'lost'. Stock up on various sizes when they're cheap.
Lands End have some, but the quality matches the price. Still, down vests for $9.00 in the off season are hard to beat.
I also just bought some Columbia shirts and zip-offs for my kids (11 &9) These are the first zip-offs I've found that actually work. Quite light weight. Not too many stupid pockets. Leg zips above the knee, not on it. They wore these every day on a week long hike and liked them.
Hope some of this helps, Rod