This past week we had a great time introducing Ava to her first cousin, Ian. Lacking any evidence to the contrary, we will say they got along perfectly. Ava was quick to help with rocking (pushing, bouncing) the baby to sleep, stroking (slapping) his face, and kissing his forehead (something that, for Ava, involves teeth). We soon learned that Ava is highly vigilant, as she took to studying him intently whenever she remembered that he existed.
We think they're going to grow up to be very good friends.