If you just have a few children and they are sitting with their parents having a goodie bag with activities for the children at their seats keep them entertained while adults have dinner and toasts are going on.
Creating a playroom is a fabulous option. If you are able to provide a separate room at your venue that can be a “hang out” for the kids will keep them plenty busy. A few ideas to have include coloring books, games, puzzles, supplying beads to make necklaces they can take home or other arts and craft projects. Most caterers will provide a kids buffet with all the kids favorites, and even can make the table kid friendly height. Once they have eaten their dinner and crafted their hearts out, a TV/DVD player to play movies and giant pillows and blankets for them to crash on is the perfect end to their night.
It is also important to delegate someone to watch the younger guests throughout the reception if you have a playroom out of sight. There are many professional nanny services, or you can ask your hotel if they have a company they work with are a few ways to find someone the parents can trust watching their children.
If you do decide to go the “adult-only” wedding, that is okay too. It is a way to keep your guest count lower, and it really depends on what you want and how you see your wedding. Some venues or decor installations at weddings are simply not child friendly, so sometimes it is a safer option to opt for the adult only. We have seen many a centerpiece or cake go down because of a curious little one. Out of town families might still choose bring their children along though and make a vacation out of your wedding, so providing off site babysitter/nanny options is always helpful. Make sure that you specify that you are doing an adult only reception on the wedding website as well as the invitation. A simple "please join us for an adult only reception immediately following" on the reception card is an easy way to make it clear.