Wow. I would never make such an announcement - the children are every bit as much a guest as anyone else at the wedding. Really? kids have to be "attended to" on a dance floor? They are people not pets.
I don't agree with the helpless attitude many of you have with regard to kids at weddings. When that is the situation - I do something to engage the kids and give them some focus. It makes it equally enjoyable for them while giving the parents and adults room to enjoy the event as well.
I am not a babysitter....it is not my job to "engage" kids, it is the parents job to keep them under control.