Best Way to Upgrade Grandkids MacBooks With My Copy of Lion from Mac App Store

I purchased a copy of Lion back in 2011 to upgrade my Mac Mini. Recently, I purchased a couple of used MacBook 4,1s from OWC for my grandkids to use (new Middle Schoolers). I've upgraded them from Leopard to Snow Leopard and bumped them up to 4GB memory. I'd like to take these units to their software maximum which is Lion. My original copy is still available for download from the Mac App Store. I'm wondering if I can download a copy to each of the kids MacBooks or if I'll have to purchase additional copies. Any experience with this. Thanks!