My 10u did wears volleyball knee pads under her pants. We had the same issue with the sliding pads. She says they are very comfy, and fit well. Also wears sliding shorts.
If your looking for a Demarini, you can follow this link to their demo house page. They have reps that will let you try a bat for a week for free, deposit required. We did this before I purchased my DDs last bat. Just find your local rep...
Composite bats are made of all different typys of material additives. It depends on material being used. This also makes a difference on how ball pops off of bat.
I agree with coach James. I got my daughter on a better 10u team for a season whereshe sat quite a bit. But now that she is working with girls again from her old all-star team, there is a big difference. I was bummed to see her sit and not play her desired positions, but she improved greatly.