Biting them. I can't help it. I have a killer case of cute aggression. “Tears of Joy” May Help Us Maintain Emotional Balance - Association for Psychological Science) which explains my strange response to adorableness better than I ever could.
I just can't resist taking a few nibbles. I try to get in as many as possible before they get teeth and start reciprocating. Unfortunately both of my children are showing signs of being just as violently affectionate as I am, so I need to be constantly vigilant against counter-attacks.