The upper Franklin canyon reservoir!
If you live in West Los Angeles, this is a great weekend or even late afternoon hike. Now, to get there is just a short drive away.http://en.wikipedia.org/wiki/Franklin_Canyon_Park. If you have the desire to be out in the country, go there and you feel like far away from the big city. It is just a magical place. If you have kids, prepare a little picnic and take them to this park. There is a little side pond with ducks and turtles and a bunch of picnic tables. So great for kids to just enjoy nature. Not much needs to be done, just let them enjoy and they will find things like, bugs crawling, ducks swimming, turtles hanging around, squirrels scurrying around.
I used to take my kids to this park and we had a blast, by just being there. We used to walk around the big reservoir, which will only take about 30 minutes, but this 30 minutes will be so enjoyable and pleasant both for you and your kids. Try it sometime and you will be amazed at this little oasis in the middle of our city jungle.