the tease and his sister

Within the last 6 months, Simon and Penelope have been developing a typical sibling relationship.
You know, the constant bickering, teasing, crying, competing and so on.
BUT- tonight, I witnessed a sweet event. Simon reading to his little sister that he adores. Love this!
And yes, I was stunned to find that Simon read me the book without hesitation. I love this age and their ability to amaze! When did he learn all those words?!