I did not do the sand so can't comment on it. But I did do a shallow swimming area for our grandkids when they were small. It turned into a filamentous algae nightmare. I ended up digging it out deeper best I could with a back hoe.
Thing of it is, the small kids hardly used it anyway. We have a nice dock extending out into the pond with a ladder to get back up. They always ran and jumped off the dock.
My vote would be forget the swimming beach and instead spend the money on a good dock to swim from. But it is your pond, your dream so by all means make it the way you want it. Just my experience.
Another bit of experience: docks are easier to build before the pond fills with water.
