I recently took advantage of having four strapping men round to lunch (with their partners) to move our very large outdoor table off the patio. Revealing a moss, alge covered set of paving stones which I am currently blasting with a pressure washer (Karcher, fabulous). I intend to turn this into a back yard kinda thing for the children to play in. I am all about giving my children more fun, outdoor things to do. It has, of course, absolutely nothing to do with them but everything to do with the inner child in me who was brought up in a two bedroomed flat WITH NO OUTSIDE SPACE.
Anyway. The therapy has been booked and I'm working through it. In the meantime, when I went to some friends for lunch recently they had a set of giant crayons and the children were going crazy graffiting all over the yard (I love the word yard, it featured large in my childhood stories of Mrs Piggle Wiggle). I got these which are really bright chalks rather than crayons (not sure why they are called crayons) but all you need to know is that they are REALLY BRIGHT, fun, and it says washable but I like to live dangerously and haven't tried that yet.
I paid 10p under £7 for a packet of 15 from Amazon. I think these are a perfect thing for your children to do in the autumn.