My soon-to-be-10 year old (tomorrow! Where did THAT decade go?) is getting a kindle for her bday from my parents. I'm not really super concerned about the erotica bit, as all the records of what gets downloaded will be available to me. I wouldn't be ok with getting her one if I didn't trust her to a-not dl anything inappropriate, and b-not dl anything she can't afford. She is really responsible about this type of stuff.
If she wasn't, I might have a conversation about honesty, accountability and what would happen if there were a concerning amount of "accidental" downloads.
My mom and I share a kindle account. I read on my droid or my netbook and she has an actual kindle. When I go online (her account, I pay her back or half of books we both read, etc.) she usually txts me within 10 minutes "just checking, did you just order a book?" because she gets the email confirming it.
anyway, hth. My daughter wasn't super interested in the ereaders for a long time because "I like paper REAL books!" and "kindles might put libraries out of business!!!" lol, but she's over that now.