"It started [for us] around the same time, and I don't think one of us wanted it any more than the other," Pratt, who stars in the upcoming "Guardians of the Galaxy," told People recently.
"She would say, 'How do you feel about that?' and I would say, '…I've been kind of thinking about that too! I think that'd be cool. Let's make that happen.'"
Then their son, Jack, was born nine weeks premature in August 2012, and the couple felt helpless.
"We were scared for a long time. We prayed a lot," Pratt, 35, said about the month Jack spent in intensive care.
"It restored my faith in God, not that it needed to be restored, but it really redefined it," the actor continued. "The baby was so beautiful to us, and I look back at the photos of him and it must have been jarring for other people to come in and see him, but to us he was so beautiful and perfect."
Now, Jack is now approaching his second birthday and Pratt calls him "a fighter."
"He's amazing," Pratt says, laughing. "He's so open and there's no fear in him no matter what."
The proud father added, "He is so charming that my plan is to just let him take care of us as soon as he's old enough."
Pratt's "Guardians of the Galaxy," backed by ABC News' parent company, Walt Disney, opens Friday.