Yes, I would (and have) gone and had the kids babysat. We took DS when he was little after asking if it was ok as had no sitters (family wedding hours from home) but now he's over 2? No way would I take him unless he was specifically invited.
I agree with PP that weddings are adult affairs. I had kids at my ceremony but not reception (except babies) and am not offended now I am the one with kids if they are not invited. It's not my day anymore, and the bride and groom are entitled to invite who they want just as I did for mine.
If having 20 of their friends kids there means they have to cut the guest list or pay an exorbitant amount for food for them, then I think it is wrong of parents to just expect kids to go.