Finn especially seems to like the guitar. Here he is playing with Daddy tonight:
Now, this seems significant to me in several ways. First of all, check out those fine motor skills! Also, he seems to be trying to mimic Daddy. And it seems to me that there is some pretty impressive cognition going on here: I think a lot of babies would just happily bang on the body of the guitar. But Finn seems to get that in order to get that sound he likes so much, you have to pluck the strings.
I'm not saying this means my kid must be a genius or anything, but look: he's engaged. He's found something that gives him pleasure and he's figured out how to manipulate it to make it do what he wants it to do. I think this is pretty meaningful.