As a Local I recommend all my Vegas Visitors go here, and we regularly take the toddler out to wear him out as best we can. This is one of the greatest parts of living in Vegas; getting the $30 pass and coming out here every weekend.
The 13 mile drive itself is worth the admission. Pulling over to climb around on Calico I or II (the first two trails) is excellent if you're short on time because you can climb on the formations, be essentially "on" the "Red Rocks" and never be too far from the car. Drive up one more to Calico Tanks and now you're hiking. Turtlehead will provide a reasonable challenge for the average hiker. The Children's Trail has a few minor educational setpieces but is really just a super easy trail. All of it is beautiful.
One protip is that if you want to hike past the picnic area at mile 8(ish) and you have a vehicle with good clearance (think SUV or trucks) you can park quite a bit back from the picnic area and save some rocky walking, but the road's not maintained: driver beware. La Madre is nice and fairly easy.
All of it is beautiful. The only negatives are they don't have food and the cell phone reception sucks. Also if you go running or biking on the 13 mile loop here go during high traffic so you don't get vehicularly manslaughtered by some errant driver.