I may do this as well, but playing it by ear to see who is actually bringing their kids. If there are only a few, I won't make a thing of it but I don't want to bust my budget paying for people's kids at the reception.
I'm also considering coordinating among our guests bringing kids to bring an extra person on the trip to be a babysitter. I've thrown the idea out there and most of the parently would gladly split the cost of one person's trip to have an option for some adult time during the trip!
This may sound a little harsh... children are invited to the DW, but we requested the wedding day to be for adults 16+ only. Our resort has a kids' club & childcare