Two bits of advice from a liberal Catholic:
1) If you're not familiar with the Catholic mass and aren't feeling a really strong "tug" in that direction, I wouldn't recommend a Catholic church as your first church visit. The Catholic mass is not terribly welcoming of visitors, in my experience, compared to other congregations. (Non-Catholics are not invited to share in the Communion table, for example. And smaller things, too, like the fact that it is assumed that everyone there knows all the prayers - you usually can't find them written down anywhere in order to follow along with the service.) If you have some familiarity with it already, however, you will be pleasantly surprised by how welcoming the worship environment is for children. My church doesn't even have a place for crying children - the priest just talks a little louder to be heard over the screaming. It's a great, rowdy place for families - we love it.
2) You may want to start with something a bit less formal than a church service, if you're looking to rub shoulders with religion but feeling unsure about a "stiff environment." You could look into something like a Bible study, or a women's prayer group, or a religiously-based volunteer program. I've been able to stick it out through a lot of horribleness within my own church (I mean, honestly, I'm Catholic) because of my spiritual "home" within our local Catholic Worker community. It's a bunch of free-range radical intellectuals who are together because we share a desire to live out the Gospel in a gritty, real way... and heaven help anybody who stands in our way. Anyway, getting to church through one of these "side entrances" may make it feel less overwhelming to choose a place to go. A Bible study is a little less threatening (usually) than a whole churchful of people on Sunday morning! And it gives you a chance to ask some questions and feel out the beliefs of the group.