nak- I don't have it in my yard, but a local playground has rubber mulch and it is HOT. Unbearable in the summer.
Another alternative might be pea gravel.
"Someday, I am going to go to bed without toys on the floor and sippys in my sink. Things will stay where I put them and I can have nice, fragile items on display. But when I do, I will look around with a wistfullness in my heart and miss the days where vibrant imaginations ran wild and there was evidence of life happening around me all the time!"