You've been there, right? At a four-year-old's birthday party, when the presents get opened as the partygoers sit around and watch? It never fails---minutes later at least half of the room is in tears, kids fighting over gifts and parents apologizing for the bad behavior.
If you're hosting a party that involves gift-giving, do yourself and your guests a favor and open the presents later, after all of the guests are gone. It is good etiquette for young and old alike and for a few reasons. First of all, it keeps the focus on the actual party and the guests. Second, it avoids any awkward moments for your guests if there are duplicate gifts, or if there is a wide range in size or value. Nobody should ever feel bad about the gift they brought, especially as it compares to others. And finally, opening gifts later allows the recipient to enjoy receiving each gift individually with no time constraint, no moving quickly to the next gift and the next in order to have time for cake and ice cream and pinatas and karaoke.
Think about it---gifting is a very personal tradition. A gift is selected personally and should be received personally. During the party, have a table set up to collect the gifts as guests arrive and then leave them put until everyone is gone and the guest of honor has a chance to take a breath and focus on each gifts individually and at her own pace. Acknowledge each gift later with a thank you note.
It's a good idea whether you're four or forty. No more party tears or awkward apologies. Trust me, you'll never regret adopting this practice.