Letting Your Kids Go

As a mom, I struggle with letting my kids go.

I thought the more kids you have, the more you loosen up, apparently not the case with me.  It's a constant struggle with worrying about them and their safety.  My kids pay no attention to what's going on around them.  We have just recently started to let them play in the front yard and go ride their bikes without us out there.  I'm always worried that they are just going to walk in the street to get their ball or for some other reason.  I hear about kids getting hit by cars or children being abducted and it just makes me want to hold on tight.  It's hard to find a balance in how much we should let them do on their own.  My kids come to me and want to go to someones house to play that I don't know.  How am I suppose to let them go and know they are safe over there?  I remember going to friends houses as a kid and my parents had no idea what was going to when I was there.  I want to hold on to them as if they are still my toddlers.  I guess this is just part of them getting older, I'll have to learn to loosen the reigns a little.
I'm writing this while my two oldest children are at their friend's houses, one I know and one not so much.  This is where the trust factor comes in that we have taught our kids what is appropriate and not appropriate.

I can't imagine what it's going to be like when they are grown and going off into the world. 
I'm sure my mom was just as worried about me, especially since I was a bit of a wild one!