My boys are a bit older than your children now, but we have a few acres, and we're in Texas. I don't think the wind ever stops blowing here. My kids are always outside. We wanted to set things up so the same way you want to. Our boys are outside all the time, and they are able to put things away easily so that it's not cluttered; we can easily mow around everything.
We have a trampoline, a swingset, and a basketball goal; everything else is put away whenever they are finished playing with it (oh, they also had a sandbox when they were younger). We have a toybox - one of those heavy-duty plastic ones- in the garage that they keep all outside toys in (balls, gardening tools, cars and trucks, etc.). One of their favorite things is a hammock that is hung between two trees outside the kitchen window. They love the hammock, and have loved it at all ages! My dad also helped them build a tree house a few years ago. If you stay there, that may be something to consider. When they were the ages of your children, they had an outside playhouse that they LOVED! It looked like a cabin. :)
Have fun playing outside!