For a nice, fairly moderate hike in Westlake Village, take Triunfo Canyon Road south to Highgate Road and head up to the southeast endpoint of Highgate, past Hillsbury Road, to the end of the road, where you'll see a trailhead sign.
It doesn't actually say "Lake Eleanor Open Space Hike" but this is indeed the way to get to this trail maintained by the Conejo Open Space Foundation. Walk past the fence on the pavement, and about 60 steps, the trailhead is on the right. There's no sign. In fact, I've never seen any signs indicating which way to go on this trail. But once you reach this path, for the most part the trail is pretty obvious. COSF has some helpful images and a trail map at www.cosf.org/website/html/lake-eleanor-open-space-hike.html.
There are some brief, slightly challenging hilly sections on this hike, along with some rocky sections, but for the most part, this trail is perfectly fine for all ages. I generally wouldn't recommend strollers on this trail though because of these sections, but if you have a solid off-road stroller, it is possible.
On the left you'll see the beawutiful Las Virgenes Reservoir for most of the 1 1/2 mile hike (about 2 1/2 to 3 miles round trip).
Towards the endpoint (Denver Springs Drive), on the right you can look down towards Westlake Boulevard/Decker Canyon and see the eight acre Lake Eleanor. Pretty cool to see from above as it is not accessible to the public.
Lake Eleanor along with the Lake Eleanor Dam (also Banning Dam and surrounding 529 acres of open space has been named City of Thousand Oaks Historical Landmark #9. More info at ci.thousand-oaks.ca.us/living/historical.asp.
I love this little hike. It is quiet and peaceful and the views are just wonderful up here. And you are just minutes from civilization.