When we bought our house there was a 3 foot by 8 foot opening in the cement outside our kitchen window which otherwise would have contributed to the beginning of a small patio. What was curious to us was that this hole was filled with lava rock, making it useless as part of a patio or as a planting box. We pretty much ignored it for a couple of years except for spraying weed killer every few months and pulling out the dead weeds a couple of weeks afterward.
It took our son Lee to finally actually sit down and rock by rock remove all the lava rocks, dumping them at the south side of the house where they at least aren't hurting any little feet. After the rocks were removed and the resulting hole covered with a weed barrier, Carolyn dumped several bags of playground quality sand into the hole. I had my doubts but they appear to have been all for nothing.
One of the most favorite outdoor activities for our grandchildren is playing in Grandma's sandbox. Depending on the heat and the intensity of the sun, the grandchildren may add to the experience by running the hose into the sand box for a few minutes. Since it doesn't drain well, there is the danger of making things too muddy.
You'll notice in these pictures that Tim and Jake are fully accustomed to the whole experience of climbing in and playing with the sand while Camdan is still a little hesitant to leave the known world of the concrete.
Having the concrete pathway helps keep most of the sand in the sandbox. We simply sweep most of it back in and spray the rest. We can usually get help from the kids with both of those activities.
Meanwhile the adults enjoy the fun of having the kids out of the way but totally in sight.