Probably better for a 12 year old than a 10, or a pretty husky 10. My son is thin, and it's huge. Bigger than all other 10-12 athletic shorts by other brands we have. They're also much longer than I expected from the picture here on Amazon, but that's actually a good thing.
Other than this, the dry-fit fabric is pretty thick and you can not see at all through it. I like that as it seems it will be good for the cooler summer days. There are also good deep pockets on both sides, which is a nice addition.