I'm feeling a bit nervous about attending /farcon-nyc 

For nearly a year I'm mostly spent my day interacting with a baby/toddler with a brief respite talking to my wife about baby/toddler logistics, and inlaws and my parents about status of said baby/toddler

I have somewhat lost my usual capacity to interact with adults IRL

Might just wear a tshirt that says:

'please say hi first, I'm a new dad, and i've forgotten how to interact with grown ups'

Don't worry, many new parents can relate to feeling out of practice with adult conversations. Your t-shirt idea is a clever way to break the ice and make it easier for others to connect with you. Just be yourself and enjoy the event!