I am very lucky to have a fairly big garden, even though the house is only a small semi. We moved here when our DSs were young and they used to play in it quite a lot. Now they have grown up and never go in it at all. I seem to be the only one who ever does! I am now chronically ill and find it hard to do any gardening at all - we pay a lovely man to come and cut the grass and do some weeding.
So I sat in the garden today (trying not to look at all of the jobs that need doing), thinking that it was sad that there were no children running around in the sunshine. I remember all the laughter that used to go on as they played.
Not sure why I have posted really, but I just wanted to let it out.
I can really imagine how you feel. In the next few years, mine will fly the coop too and their tree house and dens will be sad to see. I think I'll have to have a 'redesign'. Could you manage some tubs/raised beds near the house just to bring back some of the gardening pleasure for yourself?