The Law & Order star's wife Addie Lane gave birth to a little boy on Friday (09Mar12). The couple has yet to pick out a name.
The tot joins sister Charlie Ballerina, who is two.
He kept fans abreast of the delivery via Twitter.com, writing, "Just bought a teddy bear to give to my daughter 'from' her newborn brother. I'm considering drizzling some placenta on it for believability," and adding, "Don't tell my wife I had two glasses of wine while she had an epidural."
Sisto then gushed about his baby boy during an appearance on breakfast show LIVE! With Kelly on Wednesday (14Mar12), but confessed he's struggling to come up with a name.
He said, "My wife is stressed about it, but I'm hoping something magical happens... that makes me think, 'Oh, well of course this is supposed to be his name.'
"We got an extension at the hospital, but on Friday we do have to go down and put something in, so if we don't have it (name) by then, I think it'll be Baby Boy."