I was involved in a huge community-built playground project. I'll tell you how it was done on our project and you can modify as you see fit. After grading the site, we put down a layer of geotex. We then layed a gravel base then another layer of geotex on top of that. Topped it of with 12-18" of playground bark. The sides were built up so they are above grade. Now, this is a huge public playground so that's going to be overkill for a private yard but I'd definetly put down a layer of fabric in this application.

Preparation for the areas to receive sod: smooth the grade to receive sod. Where the sod will meet existing grass there should be about 1" grade differential. Since the differential is little, depending on overall grading you may ignore it and "heal" the difference with loose soil on top of the existing grass, blending it. It's not necessary to remove 1" soil over the whole area ... only near the edge to be blended. Don't miter corners. use square butt joints. Hopefully, you're using 6" x 6" timbers. If that's the case you'll need only one layer of timbers to form the edging. Here's an method of how you may pin them to earth so that no connectors show. I'm not labeling the sketch; hopefully you can follow along. First, set the timber framework in place as it will be in the end, so that everything is in plane and in line. Carefully roll each timber outward so that its bottom is at the top. At 6" from each end and at the center, pre-drill a hole to 3" depth and drive a landscape spike (8") into it so that 5" of the spike remains exposed. (The hole must be a smaller diameter than the spike so that the spike is driven very tightly.) There will be 3 spikes embedded per timber @ roughly every 6'. Then, at the setting bed for the timber, dig a 6" dia. hole with clam shell post-hole digger, that will correspond to the location of the spike in the timber. The hole should be about 15" to 18" depth. A little more or less is inconsequential, but it needs to be below the frost line. If the hole flares slightly at the bottom it will keep the concrete from lifting upward later. Mix some concrete so that it flows but is not runny and fill each hole with it. Don't overfill. Roll the timber back into place so that each spike is aimed down into the fresh concrete. Adjust so that it is perfectly in place. Try to dig the hole depth so that is accepts about 25 lbs. (half of a small bag) of concrete. A little trial and error will help develop consistency. At each corner, pin one row of timbers to the other with a spike or lag bolt in a pre-drilled hole. This will keep any separation from happening at the corners. I'm not saying this is the only way to do this. It's A way that secures the timber from both horizontal and vertical movement, without holes and re-bar showing. The mulch is installed after the play equipment is installed.

Soooo...is it done yet, Chevy? :-D J/K, of course. But I don't think I'm the only one eager to see your playground garden evolve. I was taking a mental inventory of my vintage outdoor-able toys, and am sad to say I think I sold my little red trike last summer. :( But I do have a rusty red wagon and a mini wheelbarrow, and who knows what else. I have a couple of big old metal toy trucks, but they're in really good shape so they'll probably stay inside. In December I display them under the Christmas tree along with a metal erector set box, old skates, and some other odds & ends. I am overjoyed to finally find a place where other people think like I do. My family and friends roll their eyes at me and my hobbies, you know. HMPH!

Great start! All you need is a kid's sand shovel & you're good to go for the toys! Can't wait to see it finished!! I have wagon just like that full of plants. I think my dad got me some tires from garden shop as wheels are 1st to go on those old wagons. Jan