For older gens of tweens, going to the mall meant a trip to Limited Too for glittery graphic tees, Rue 21 for sparkly accessories, or Claire’s for ear piercing parties and walls of lip gloss. It was the defining stage of girlhood that celebrated being “in-between”—not quite little kids anymore, but not full-on teenagers either. Now, tween girls don’t really have as many stores made just for them as once-popular mall staples are gone or fading. Tween girls are instead looking up to teen or young adult influencers and older Gen Z, gravitating toward products like Stanley cups, Sephora hauls,...