Grassi Lakes is a fantastic short hike at only 4.3 Km. Perfect for first timers who have never been to the mountains, or for anyone with children. It's about 45 minutes up.
I've been quite a few times over the past couple years. It's also a great place to go solo with a book and a snack.
There is usually lots of parking unless it is mid day on a weekend. It is very well trafficked and the parking lot has washrooms.
A little ways up you will have the option to do the "easy" or "hard" rout. I recommend doing the hard rout if possible as it is more scenic and still easy enough with the handrails and built in rock stairs.