Personally, I wouldn't have a small child using headphones. The speakers would be out of reach but I don't know that it's necessary to automatically assume that a 6 year old will trash the equipment. I have customers with a 5-1/2 year old and a 2 year old. The daughter turned 3 in March of '07 (I finished installing the system in May of '07) and I used the Harmony 1000 remote. If she wants to play a DVD or watch TV, she knows how to turn it on, off, operate the transport buttons and change the volume/channels and use the DVR. Other than the DVR, she has had no problems using the rest since that summer and AFAIK, she has never cranked the system up accidentally, scratched anything or damaged anything intentionally, although she (and others) have accidentally dropped the remote a few times. No fingers through speakers or grills, the discs are pretty clean and she informed her dad while I was there that she didn't like going to her cousin's house because she didn't like the way their system worked. Just a bit precocious.
The 2 y.o., OTOH, recently decided that the DVD Rom drawer on their ReQuest music server didn't have enough discs in it, so he slid two more in.
If this was my child, the speakers would be mounted high enough that they wouldn't be damaged, but they would me mounted securely, or in/wall or ceiling. The receiver would have a way to control the maximum volume and I would program a cheap remote to control everything. DVD players are $35 new, so that wouldn't be a big deal, for TV and listening to CDs. A Sherwood receiver is cheap enough and a hands-on instruction session would include what happens if the volume is cranked too high (consequences for her, not the system).
