They do the cornrow braids, like those found on a cruise or in the islands, at the hair salons. IIRC the Boardwalk, GF, Beach Club, Contemporary and the Dolphin all have a salon. You don't have to be a guest of the resort to use the salon but I would recommend making a reservation.
FWIW, I had my girls done here at home the day before we left, it was cheaper and I didn't have to spend vacation time doing it!!
Most of the resorts as well as MK, AK and the Boardwalk area also offer the hair wraps. Colored string and beads wrapped around a strand, my girls had one done at the Boardwalk and it came out great. My youngest had hers done in December and it lasted until late February. $1.50 per inch for the wrap plus the cost of beads.
TJ