Tips for building a children's sandbox include making sure that the ground is level, placing the natural curve of each board of the frame facing into the sandbox to prevent warping, and using leftover pieces of the wood from the frame to create triangle seating at each corner. Corner seats also provide extra structural support. Landscape fabric, pressure-treated plywood or wooden slots are weed-protection options for the bottom of the sandbox.
If using a plywood bottom, another tip is to cut two pieces the same size, one for the sandbox bottom and another for a removable top to keep animals out of the sand when the sandbox is not in use. For the cover, drill two holes 6 inches apart on each side of the piece of wood. Stringing and knotting marine-grade rope through each set of holes creates handles for easy cover removal and placement. For shade, leave room behind one of the corner seats to place a short piece of PVC pipe and drill a hole in the sandbox bottom so that the pipe fits snugly through the bottom. The piece of pipe becomes an umbrella holder.
If it is necessary to create a flat space for the sandbox, start by marking out the sandbox dimensions and find the lowest point inside this space, digging out earth until the entire space is at the target depth.