Essentially what I'm looking for is to avoid these two ends of the spectrums:
1) Not a dive bar.
2) Not a five-star restaurant.
It is obviosuly in the restaurant's best interest to cater to families with kids. Which if you have infants, it can get a bit tougher and depending on their temperment, you might just avoid eating out altogether, but for 2+ year olds, means high chair/booster seat preferred (strapping in your younger kids is a fricking God-send), and crayons/paper + kids menu is bonus. Also, because I have this hangup about taking my daughter into dirty bathrooms, the place should have clean restrooms, or at least appear to (that's just my phobia more than anything though).
Re: playpens-- I just went on a little vacation with my brothers' family and their kids and mine, and we found this cool place with a beach-like sand area outside-- where we could all sit and drink margaritas in the sun and watch the kids at the same time. What a grand time.