That's an excellent play area, I hope they appreciate all the trouble you are going to. We don't use any weedkillers in our garden, otherwise there wouldn't be many plants.
Our 'lawn' is mainly clover and moss - nice and springy to walk on and the clover is in flower and attracting the bumble bees, meanwhile the skinny bees (don't know what they are called) are all over the marjoram flowers along the path.
The weather is lovely and Casper is spending lots of time in his Magnolia tree. https://1drv.ms/v/s!AiShclt2ghrmhDgJxPbKxK2eFHkD