Wash watermelon under cool running water and pat dry. Placing watermelon on its side, cut off the bottom end by 1/4- to 1/2-inch so it can stand flat on its end. Be careful not to cut too deep into the white part of the rind — this would allow liquid to leak from the bottom of the carving.
Stand watermelon on cut end. With dry erase marker, draw a line about 1/3 of the way down from the top, around the whole watermelon. Pick a point on the line and find the corresponding point on the exact opposite side of the watermelon.
From those points measure 1 inch to the right and to the left. Connect those points by drawing two parallel lines across the top, forming the shape of the handle. Use a paring knife to cut along lines, being careful to not break or crack handle.
For best results, hold the paring knife like a pen, but only cut halfway into the rind. Once you complete that first cut all the way around, go back and cut the rest of the way through the rind. Doing the cut in two steps will ensure a cleaner line and smoother cuts.
Carefully remove trimmed rind and flesh. Try to remove as much as possible in large portions that can later be sliced and used with the cookie cutters.
Scoop out remaining flesh from base, trying to leave as much flesh intact. Remove it in larger pieces that can be used for making watermelon balls or bite-sized chunks.
Take knife and carve a channel about 1 to 2 inches from top edge, creating the rim of the bucket. Take the large removed pieces and trim off rind. From flesh, cut rectangles about 1/2 inch thick.
Using cookie cutters, cut shapes from watermelon. To create light-colored shapes, use slices of honeydew melons, or cut decorative pieces from white part of watermelon rind. Set aside and drain on paper towel.
With remaining fruit, make either cubes or balls and drain. Toss with other cut fruit and berries and fill the bucket.
Decorate top of bucket with cut watermelon shapes and new, clean toys and shovels. Use light-colored cake mix to resemble sand.