No one's saying you need to have a Happy Meal at every child's seat, but it's worth investigating whether your caterer can provide kid-friendly menu alternatives. Although some children might enjoy the filet mignon and asparagus that the adults will be eating, younger munchkins are more likely to scarf down a plate of chicken fingers and french fries.
If you're going with a buffet instead of a seated dinner, there will probably be some kid-friendly options somewhere down the line. Kids might go crazy for cheese and fruit platters -- or even a fancy ham and cheese from the carving station. It's nice to cater to kids, but the more options you provide to all your guests, the more likely there will be something kid-approved.
Be sure to ask parents about any food allergies their kids might have. You want your guests to safely enjoy their meal rather than making a dash for the nearest emergency room.