To clarify my rating: I'd give it a 3.5 if I could, but I can't, so I'm rounding up. And that 3.5 is for people with kids. For people without kids it would probably be a 1, but really I can't imagine that you'd even be considering this event if you didn't have time to kill with the small people in your life on a weekend afternoon.
With these qualifiers in mind, I'd say the Popovich Comedy Pet Theater is pretty darn good in a non-standard kind of way. First of all, it's not just about pets. In fact, I'd say it's not even mainly about pets. At least half the show is Mr. Popovich and a pack of young acrobats acting out old-school comedy skits. Then there is a pet segment. Then juggling. Then more pet tricks. Then flipping and handstands. Then more pets.
The props have a very home-made and kind of old feel to them, and the pet tricks are not all that amazing, but the animals are cute, and for your kids that will probably be enough. Plus it's pretty fast-paced (good for short attention spans), and the acrobats are very talented. Go early, let the kids run around in the big grassy area outside the theater beforehand, see the show, then go to dinner in Westwood after. Perfect way to spend a Saturday. Oh, and spring for the good seats--they're cheap and it's nice to be close to the action.