I can honestly say I've never had to hide any books from my parent's.  They always encouraged me to read whatever I got my hands on.  Mom wasn't too pleased when I read my grandmother's romances at ten, but given the fact that our books were in transit, it was better than nothing.  My parents were pretty cool about reading.  I think they realized it was either let me read or deal with the havoc a bored ADD kid could create.