Norman Keeps
"One of the first kinds of castles in old England was the Norman keep. It was a simple tower with its one entrance high above the ground."-Jan Adkins, The Art and Industry of Sandcastles
My daughter taught the little boys that there are two kinds of sandcastle keeps you can make.
The first type is a rectangular keep and is made by mounding the sand into a tall pile and then using a trowel or large sand shovel to sharpen the sides to flat with rectangular corners. 
Sometimes you need to add wet sand to the sides with a trowel. 
This strengthens the sides. The round-sided keep is made from damp sand packed lightly in a sandpail and then turned out. It might take some practice to get your sand with the perfect amount of water added so that it turns out of the pail and yet stays together without crumbling. It will vary, too, according to the composition of your sand.
Once you have made your keeps to your satisfaction, it is now time for crenelations."Crenelations, behind which defenders duck to avoid arrows..." -Jan Adkins
Crenelations are best made by cutting down on either side of the outcropping and then lifting the portion of sand up and out.
Norman Keeps for your imagination to play in.
