This 12" high child's wood stool is easily made using stock dimensional lumber (standard or closest metric size) all cut at 90 degrees and assembled with glue and nails/screws. The overlapping joint technique is simple, direct, and strong. It's versatile and adaptable to many designs -- see my blog for lots of other stuff. http://furnituredesignbank.com

Step 1: Exploded View

Use this exploded view to create your cutting list. You can make this stool longer, more bench like, or even deeper by using different stock lumber seat planks -- like1x3's for example, and then there's plywood or anything handy and recyclable -- it's the overlapping joint that counts.

Step 2: Tools

I used a chop saw, but a hand miter saw and a little elbow grease will also do the job. A saber saw can work if you can make a straight cut; I never can seem to do a great job with mine. The more clamps the better. I used 1 1/2” wire brads, but 3d or 4d finish nails are good. I
also used #6 square drive wood trim screws to attach the side skirts, but nails work there, too.

Step 3: Cut, Sand & Mark

Sand/ease all exposed edges now. Mark the ends and best faces. Drill any pilot or clearance holes to prevent splitting near the ends.

Step 4: Make Two Leg Assemblies

Clamp a long stop block to a bench and use a smaller free block on the sides to locate the legs and skirt flush.

Step 5: Check the Square

This is an important step which will save you grief later. Do it immediately while the glue is still wet. You can usually budge the legs a little. And wipe off any excess glue while you're at it.

Step 6: Add the End Skirts

Working work upside-down, fasten the end skirts to the leg assemblies. Keep everything flush. I used screws (with drilled clearance holes -- not pilot holes). Nails will work if you can prevent the frame from bouncing around. If you have enough clamps and time, just glue it and put in the nails/screws later. You should have a mechanical fastener to prevent the wood, under very high stress, from tearing away with the glue. As soon as you can, while the glue is still wet, turn the frame over and check for square and level. Add weight to the top to press it flat if necessary.

Step 7: Add Seat Planks

Use 1/4" spacers (anything is fine as long as you adjust the end skirt width) for the seat width. Since the overlap at the ends is 3/4", I clamped a scrap 3/4" board to an end skirt and used a small block to locate each plank. You can use your fingers on the sides. Nails work well here because you have the support of the bench.

Fill the holes, give it a final sanding and after the glue dries, paint 'er up with a child friendly finish. Breakout the smocks, maybe your kids will want to decorate the sides -- or the whole thing!