It's no longer a must to open gifts during a party. If children are young, if there are lots of guests, or if there's a tight schedule, unwrapping can add to the chaos; feel free to leave it until afterward. If your child does open presents during the party, talk to him beforehand about manners, reminding him that sometimes honesty ("I don't like this toy") can be hurtful. Suggest alternatives, such as "You were very nice to get this for me," or "What a great idea."
As gifts are opened, have a pen and notepad on hand to write down what came from whom (this is a good job to assign to a helper). Take a picture of your child with each gift to enclose in the thank-you note. If your child does not open gifts at the party, thank-you notes are especially important. Try to have your child write them within a week of the party, with your help, saying something specific about each gift. Knowing that it's important to thank people, and how to do it, will serve children well throughout their lives.