Before we went the first time (pre-Covid) I researched how to maximize DD's chances of being picked. The most important hint seemed to talk while waiting (when they can hear you) and tell the kid ahead of time to speak clear and distinctly. They want to put on a good show, and if the kid whispers or mumbles it ruins it for the people that aren't the kids family. I asked DD what she hoped the core of her wand would be. I figured it couldn't hurt if they knew that we were there to buy. The other hint I read was just to keep doing it over and over and eventually they will take pity on you and pick your kid. I would also have the older sister hold her wand, so that she doesn't get picked again. Pre-covid they would sometimes do a private thing after your show and before the next if you told them you were really hoping for a wand to pick her. I don't know if that is still happening. One advantage you'll have is that the groups are smaller now due to social distancing.