What you on about 'young kids'? This isn't HSM, it's actually quite an adult show. I'm 22, i know people in their 30's and 40's who watch it. I think you'll find that not many under 16's actually watch it, it's not targeted to that age group.
I dunno why the girls mash up is doing better than the boys though, nor do i know why both are doing better than Somebody To Love, which i think is the best Glee tracks so far including DSB!