It's much more important that you get a quality harness that distributes the weight properly for the kid's frame.
That being said, System Blue was doing some great things with a hybrid wood/carbon fiber drum. Those things weigh almost nothing. If you can find a set, go for it - but know that SB is out of business at this point. You can go with Ming/Mair if you want - their 14" marching snare weighs ten pounds.
I'd advise you to just go to TBA and play-test and try some out to make sure that they sound decent enough, and then get what you think is appropriate. But again, remember - the harness is everything. Don't cheap out.
And as "Retired" said - Power Lite still exists (it's a Yamaha product) but even a standard Power Lite snare weighs about the same - 11 pounds, and they aren't nearly as durable as a typical marching snare, nor are they free-floating drums the way the Mair drums are. You may not notice or care - but that's why you go play-test at TBA. Double check you can get the sound you want.