The closest play center to me has the same arrangement as you mentioned Deb, the under 4's area is fenced off and its totally padded so I can put both my boys in there and sit down and have a coffee while they enjoy themselves. I love it because I don't really have access to any good babysitting so when I need some quiet time I usually go there.
The other play center we use has more equipment and a giant bouncy slide that Yasin loves but I can't relax there because its always busy and there are big kids racing everywhere.