This morning, for the first time, BK2 pointed at me and said "du".
"Du" is German for "you" and before she had always used "Papa" to refer to me. I wonder whether this was an early one-off or whether she has understood personal pronouns.
Oh, and "du" is actually not like "you" but rather like "thou". The English language has almost forgotten about this less formal way of addressing someone, but in Germany it is very much alive.