First of all, don't spend time worrying about bike week. Repeated surveys have shown demographics of the Harley riders who come to bike week may surprise you - lots of couples, most 40+, college grads, professionals with salaries well above the median US average. Some places may get a little rowdy late in the evening, but that's mostly the bars who cater to bike week. It will get busy around the Inlet Square Mall area just South of Garden City, and near the entrance to Murrells Inlet, but just drive careful and be prepared to slow down. Our grandkids love to be down here during bike week. We find a good parking spot around SBB, near Inlet Square and admire the beautiful custom bikes that put on a non-stop parade.
Don't miss the MarshWalk in Murrells Inlet. CreekRatz is a good place with kids. The food is nothing to write home about, but it's casual with nice outdoor seating, great views of Murrells Inlet and grassy areas for the kids to play. Huntington Beach State Park is a beautiful beach and they have a very nice Education Center that's worth a visit.
The City of Myrtle Beach has taken a strong anti-bike week approach, and many of the bikers will avoid going into the City, itself. That's put a real hardship on many of the businesses within the city, but it does keep down the traffic for non-bikers who are vacationing at the same time. The new boardwalk in MB and the adjoining SkyWheel are worth checking out.
Y'all have fun!
Edited: 8:48 pm, April 29, 2012