I once went for a horse ride on a beach at Hermanus... it was the craziest thing ever! My horse was the stubbornest tough old stallion around and refused to go where I pointed him!
Our group of horses ended up walking through the waves, among swimmers, all the while with me helplessly waving people out of the way mouthing something like "Out the way, I have no idea how to steer this thing!".
The guy in the photo is one of two who offer horse rides at Big Bay's Eden on the Bay (primarily) for kids. It seemed pretty safe, and I think it'll be plenty of fun for kids.