For a baby's gender reveal party, the parents can release pink or blue balloons or have guests reveal the gender via scratch-off tickets. The parents might also reveal the gender by handing out confetti poppers filled with pink or blue confetti.
The parents can have guests guess the gender by placing pink or blue ribbons onto a chalkboard or bulletin board or submitting a voting ballot. If the baby has a sibling, the sibling can wear a shirt with "I'm getting a baby brother" or "I'm getting a baby sister." Another idea is to put pink or blue candy or confetti in a piñata.