Yes, the ocean will be too cold, but walking on the beach with the kids would be do-able. Myrtle Beach Travel Park is very nice. We have then there 5-6 times in the last 20 years....Here is a link to our Aug 10' trip
with pictures of Myrtle Beach Travel Park. I do say there showerhouses are very modern. They have both a indoor and outdoor pool. MBTP is located between Myrtle Beach and North Myrtle Beach on Restaurant Row. Off season price are much better then the $65 per night we paid.