DH and i took DD (who was 7 at the time) on a surprise trip to wdw in 2004. we stayed at a hotel outside wdw on the night we arrived, and oddly enough, she didn't notice any of the billboards on the way there (she's been reading since she was 4, so we were really shocked she didn't figured it out), so when we got to our room, we told her we were going to disney world in the morning and she screamed so loudly, we were sure the people in the room next door were going to call the police, lol. we checked out the next morning and then checked in at pop century.
funny story: since it was a surprise trip, she didn't think we'd brought her bear she sleeps with, and when we got to the hotel outside wdw that first night, she looked really sad and said "i guess i can sleep without her". i then pulled her bear out of her suitcase and tossed it to her and she screamed almost as loudly as she did for wdw, lol.
that was a really fun trip. i hope you and your family have as much fun as we did, OP!

ETA: we drove on that trip, 10 hours from NE alabama, and even when we were actually IN orlando, DD didn't realize where we were going, even though she could read the billboards and exit signs. if you want to drive, i say go for it! we usually drive at night, DD and DH sleep while i drive, then when we get to wdw the next morning, we do a little shopping, have lunch at pop century, and DH takes DD to the pool while i take a nap in our room. it usually works out really well, since we don't do a park on check-in day.