I built a simple table for my kids to play with, in their playroom. The beauty of this table is that a simple hole allows the child to play in the centre of their game, be it with Lego or Playmobil and so on. All I did was cut a sheet of half inch 8 x 4 plywood in half along the centreline. Then, I found the centre of the half sheet by drawing two diagonal lines from corner to corner. I tacked in a small nail, tied a piece of twine to it and then traced a circle with a pencil, leaving a margin of about three inches either side. I then took out the nail and drilled a small hole on the pencil line, enough to admit the blade of a jigsaw and cut the circle out. I also rounded off the sharp corners of the sheet and dressed the cut edges with a sanding block. I had four chair legs and screwed them to the sheet to make it a table. I also glued and screwed on a bracing piece about two feet long, under each of the long sides, to stiffen it up. I left it unpainted, as it's a large surface and would take too long to dry and my kids were happy with it in that condition, ie, no splinters and no screws ticking out. I also thought of making another cut out sheet half to make a side panel for kids to crawl in and out of, as my daughters always enjoyed the fact that they could crawl under a table and pop up in the centre.
materials: one 8 x 4 sheet of plywood; a few screws and wood glue for bracing pieces (also made from plywood), four chair legs or similar to make legs (kid height); sanding block; jigsaw. Construction time: about an hour.