In North Myrtle Beach, you really have no good choices east of US 17. You can go up and down Ocean Boulevard and a few of the Avenues (cross streets). OK for a slow amble but not good for training. Little River Neck Road (off of Sea Mountain Highway) is OK in a pinch. All of these roads can be dangerous any time of year, but particularly so in July, since there are lots of cars, usually containing drivers unfamiliar with the area (and who are often sunburned and/or drunk).
For a family, my honest opinion is, leave the bikes at home and enjoy the beach.
If you want to train, my suggestion is to drive a few miles inland, to (for example) Loris SC or Tabor City NC. Park somewhere and ride on the lonely country roads that radiate from those towns. It'll be flat, and hot, but it's pretty desolate back there if you stay off of US highways and S.C. State Highway 9.
Last edited by T. Shandy; 07-01-09 at 03:42 PM.