(Haven't read the other responses yet because I wanted to give my honest answer)
It's hard to say exactly without seeing the set up, but basically, yeah I think I would.
We don't even have a fence, and I've been letting my 3 year old daughter play with her sand table on the back patio. I leave the sliding glass door open and can easily keep an eye on her from the lounge and kitchen.
My only real concern at this point is the fact that some people in my neighborhood let their dogs run loose on occasion..supposedly on "accident"
. I'm thinking about getting a fence soon so she can play in the yard more freely, and I don't have to worry about them.
I'm not worried about abduction really, although it's something I am mindful of to some extent. I just don't see the real risk in playing in a fenced backyard as far that goes.