Both Frozen and Frozen II open with a scene where a young Anna and Elsa play together.
In the special features for the new Frozen II Blu-ray, Lee says…
We got more of Elsa exploring what her powers were capable of, more of Olaf being hilarious, and even more of Anna and Elsa as kids.
In both scenes, Anna is aware of Elsa’s power, so we know that the scene in Frozen II actually pre-dates the one in the first movie, where she loses that knowledge.