A family member has two daughters, one is getting married and has chosen her sisters 21st birthday as the wedding date. Apparently it was the only date available. My kids are close to the birthday sister, and a group of them were planning to tie a balloon to the birthday girls chair at the reception after all the formal parts are over. The bride found out and had their mum put a stop to it. I have just found out they have a surprise birthday party for the girl planned, all the cousins are leaving the wedding reception early and meeting at a friends house to celebrate the girls 21st. I told my kids they are causing a huge issue in the family, but they insist it’s only fair as the bride did this deliberately to stop her sister having a party. I can’t say I entirely disagree with them as the girl isn’t getting a party due the wedding. I am in two minds about it. I can tell on them and have it stopped, or pretend I know nothing. They aren’t leaving before the formalities are done, and plan to be discreet. But I imagine ten people leaving a wedding will be noticed.