Starting with The Princess and the Frog (2009), every Disney princess movie has included a scene where the princess is a child.
The Princess and the Frog (2009)
Brave (2012) (yeah, I know it's technically Pixar, work with me)
The only other Disney princess (I can think of) who was a child in her movie is Aurora, who was a baby for story purposes so that she could get cursed. We're introduced to every other princess as an adult/teenager. I have my own theory about why the trend so suddenly and uniformly arose, but I would like to hear other people's thoughts.