Even the most mild-mannered kids get antsy or yell out funny phrases from time to time.
If you want to have kids at your wedding, be aware of the risks that are involved, and make an effort not to sweat the small stuff. Opt instead to see how sweet and unique their presence is at your ceremony and reception (dollar dance with the flower girl, anyone?).
If the idea of child-related disruptions is too much for you to handle, you should probably make your soiree an adults-only affair. Just be sure to communicate this in a polite way, so that parents can make other arrangements for their little ones. According to basic wedding etiquette, make this clear by addressing the inner envelope of the invitation with just the parents' names. Should parents RSVP for four instead of two, a simple phone call can clear up the misunderstanding.
It's not the bride's responsibility to provide childcare for young guests, so don't feel obligated to do so. One courtesy you can offer is to put guests with young children in touch with one another so parents can go in together on the cost of a babysitter.