For my part, I try to project sanity and good cheer as I ricochet between feeling anxious, excited, overwhelmed, melancholy, joyful, and plain-old stressed out. Our kids aren't quite as capable of managing their emotions and can act out in all sorts of ways, with little or no warning. I fondly (not really) remember a total meltdown one of my children had under a dress rack at Macy's while I was scrambling to do some last-minute shopping.
Preparation and planning can help you keep the peace at the holiday table. These tried-and-true ideas are simple to use anytime you're getting pushback at mealtime, and are good to put into play before you show up at Grandma's house with your anxious, excited, overwhelmed, joyful family.
Let kids help with menu planning, shopping or cooking. When children have a voice and contribute to these aspects of the meal, it empowers and encourages them. It can be as simple as saying, "I'm making a shopping list. Is there a new fruit you'd like me to buy? Would you like to come with me and pick it out yourself?" or "I'm thinking about what we will have for dinner on Friday night. What would you like?" or "I'm making stuffing to bring to Aunt Jenny's house. Would you like to help?"
Make a favorite festive. Whether you are hosting the meal or have been asked to bring a dish to someone's house, get the little ones involved. At the holidays, prepare one or two familiar foods so your children have something they know they'll like at the dinner table. You can jazz it up by adding a new ingredient or naming the dish in honor of your child: "Harry's Hanukkah Apple Sauce" or "Delaney's Delicious Dip." Now the little ones have a food they helped make, named after them, that they might actually eat. Score!
Have someone else cook. I've found that many children are much more receptive to eating food someone else has prepared than to cooperating with their parents as they cajole the kids into trying something new. It's best to play it cool when you witness this, and make a mental note to offer the new food at home at some point in the (distant) future. It's also wise to have the manners discussion before your sister-in-law puts a bowl of bouillabaisse in front of your first grader (see next point).
Talk about (and model) good manners. Even the smallest children can learn to be polite and respectful, and that starts by exhibiting and expecting that behavior consistently at home. Good manners go a long way toward making dinnertime peaceful. You can role-play with your kids so they know what to say and do when presented with an unfamiliar food at a friend or relative's house. ("That looks great, Aunt Jenny, but I'm stuffed!" or "I've never had ravioli, but I'll give it a try.") Keep it light; they'll get the message.
A few books on dinnertime manners that the younger ones might like include: Suppose You Meet a Dinosaur: A First Book of Manners by Judy Sierra; Manners at the Table: Way to Be! Manners series by Carrie Finn; and The Berenstain Bears Forget their Manners by Stan Berenstain.
Take a deep breath and let it go. Of course, there are many factors that can contribute to children's behavior at dinnertime: tiredness, illness, and sensory issues, including noise levels, food textures, unusual smells, and even uncomfortable clothing. The best advice I can give is to keep calm and carry on. Happy Holidays!