Cant add much to what these guys have said.
One thing I did on my pond was run my overflow pipe from a concrete drop box for the water to go into then out the back of the box, works extremely well for keeping up with the incoming water, when the water level rises a couple inches I have a couple inches flowing into the box from three sides and fills my overflow pipe to full capacity quickly, I have an emergency spillway a foot or so higher than the box and my water has never got up to the emergency spillway in 7 yrs, with some pretty heavy rain events, in spite of having 120+ acres draining into my pond, 15 acres.
The cons to that is the water that it releases is skimmed right off the top of the pond and sometimes, in certain times of the yr, that also means losing a lot of tiny baitfish, I have added screen to the sides to make it more difficult for the babys to get washed over board.
I am in agreement with most on the beach area, its a pita to keep usable, but I can see your desire for one with the kids, it might be worth the extra effort to keep it clean. but for the most part, if not, without enough maintenance, the first two minutes in it will stir up enough sediment to make the water too nasty to enjoy.
We all picture a nice sandy beach, like at the ocean, but it really doesn't work that way here in the inland areas where the ponds fill with runoff groundwater, but again, with the kids it will probably be worth the effort, in about five yrs you will let us know that the beach has been abandoned.
