JanineA -- you are not being selfish at all. I'm actually quite suprised by the few mothers on here that are saying otherwise. Your wedding is about you and your future husband. I have told everyone coming to my wedding that it is adults only. If they can't find a sitter or don't want to leave the kids at home, then they don't have to come at all. If you don't want kids at your wedding, you shouldn't feel bad about it one bit.
Now, after having said my 2 cents, I must say that I do like the ideas that everyone has given you to keep the toddler quiet, and I think you are doing a great job at being more than accomodating