He is always so helpful and patient with his baby sister. She is never going to have to worry about anyone messing with her. "Bro bro" (what he calls himself when he talks to Ella) is always going to be watching out for his "little goo-goo-ga-ga" (not sure how that nickname stuck, but he refers to her as this a lot).
Here is the video of the diaper change. I love it when I ask him if she is going to crawl out of the diaper and he starts laughing and says "Maybe".