Accepting A Wedding Invitation And Then Changing My Mind

My coworker put out nice, formal-looking invitations at work, inviting us to a garden wedding and a dinner and dance reception. I have to work during the ceremony but I thought it would be fun to go to the reception. I RSVP`d that my husband and I would come. My coworker just told me that only a couple of other coworkers are coming so far, and there would be a lot of little kids at the reception. Now I don`t want to go, if there won`t be people I know, and there will be little kids running all over the dance floor. How do I politely decline when I already said I`d come?