Both mine loved it. We read it to DS when he was six, a chapter a night, he then started reading the rest of the series by himself from the middle of book two, got to number five (six and seven weren't out then), and went back and read them all again - all in the space of a few months, so he was about six and a half when he finished. Then read the next two as soon as they came out.
DD read the whole series in the space of about three months when she was eight, and also loved them all.
I read them all before the children, and I wasn't particularly worried about unsuitability, except for DS reading book five when he was so young - I thought the death of Sirius might upset him, but he took it in his stride.
No particular questions stand out - it just triggered a complete obsession with magic, Hogwarts etc in both of them. Oh, and DS was also intrigued with the talking to snakes thing, so it also led to a huge interest in snakes, and spending lots of time in the reptile house at the zoo (he never managed to get one to talk back, though).