Some of the resorts have hair salons that will cornrow braid but you have to make an appointment and be sure to specify - corn row braids - as not all the hairdresser's do them. Its very pricey and like another poster mentioned very time consuming. Not something my girls would want to spend an hour or more doing during or vacation. That said once its done its very convenient for a FL vacation. We have a local hairdressing school that does them quick and inexpensive so we have them done before we leave. Many of the "super cuts" or "snip it"s" places will do them as well. IMHO your better off having them done a day or so before you leave so as not to waste precious vacation time or vacation $#$. The stands in the pools, boardwalk or in the parks offer the "hair wraps" not the braids.
If you do have them done be sure and bring alone a scarf, if your dd will sleep with it the braids stay in better and fresher longer!!
TJ