This is such a subjective question that I don't know if our responses are going to be of much benefit to you. "Not sure if that is a lot or a little."... neither are we. We don't know your income/budget, or even how old your kids are.
I shopped a lot of thrift stores when our kids were little. But as teens? That doesn't work anymore. The only thing that helps (besides shopping big sales) is hand-me-downs from close friends who go to different schools.
One other tip? Try to shop for basics at Christmas and include them in wrapped gifts under the tree. My parents did that, and we do it for our own now. It's a yearly thing now that they normally expect socks, underwear, Tshirts, bathrobes, and sometimes winter things under the tree. Of course, where we live, we don't get much cool weather until around Christmas time anyway...
They don't get all of those things yearly, but it's nice to be able to throw a pair of goofy footy pajamas under the tree when your 11 yr old has been begging for them (but not needed) for a month. Or a bathrobe that is a little big so they can wear it for more than one year.
Even my husband waits with anticipation for new Tshirts and underwear at Christmas. :)
With teen kids, I find a TON of steals right before (and after) Christmas as some of the favorite clothing stores. A&E and Aeropostale both have fabulous sales and post-Christmas gift cards that you receive when you buy before Christmas. So they get some things, and a gift card, and then we go back after Christmas and pick up another couple things with the after-Christmas sales and gift cards.
The worst, for us, is shoes. Teen boys can blow through some shoes! Sheesh.
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ETA
But since you asked, we probably spend that just on back-to-school shopping. With jeans/Ts/shoes/socks/backpacks for two teens. (yes, socks are fashion accessories for teens, so they aren't cheap and don't come in bulk packs of 6 anymore). This doesn't include the running shoes for gym/sports/weight training, wrestling shoes, daily wear, boots (shop class), boots for fashion (daughter), school spirit apparel, uniforms (karate, wrestling, band), or winter jackets. I couldn't begin to guess, really. I try not to think about it too much. I have a line item budgeted for school clothes of $600 every July. The rest of the year it is part of Christmas, or the monthly "disposable" monies. Or attributed to the line item for their extra-curriculars (sports, etc).
Last spring I had to go on a hunt for an appropriate dress for daughter's piano recital (and shoes to match that are piano-pedal-friendly). She doesn't normally wear dresses, so she didn't have a wardrobe to draw from. That alone would have been 1/3 of your per child annual budget.