I got this email from Sam's teacher today:
I just wanted to reach out to you and tell you how well Sam has been doing lately. He recently has shown an interest in two of his peers (_______ and _______). He will get in their face and smile or he will pull on their shirt. It's very cute! After he gets a reaction from them, he has a big smile on his face.
Have a great day!!
This fits with what Sam seems to have been trying with his sister as well. I also caught him looking over at his babysitter's son the other day and flapping his hands like he was excited. He saw the son playing with a friend and he looked like this tiny little part of him deep down inside wanted to join in but he had no idea what to do.