The Cubs pitcher will fly on July 10 to Guatemala to complete the visa for the boy, also named Carlos. The Zambranos hope to have their new son in the U.S. by the end of July or early August.
Zambrano had gotten approval from the Cubs for the trip before he went on the disabled list with low back soreness.
"My daughters, my wife are really excited about this," Zambrano said on Sunday about the new addition to their family.
Zambrano, who has three daughters, first met the boy when he was 5 months old; he turned 2 in May.
"When I met him, he was in the orphanage and he didn't have a name," Zambrano said. "I liked that kid so much and I've been helping the foundation, Hope of Life, and the guy who is president of the foundation, he named the boy 'Carlos Zambrano.' He didn't know I liked that boy.
"When I told my wife at the beginning and started to talk about this," he said, "I said to her, 'If we want to adopt a kid, he has to be special, there has to be something that tells us he's the one, he's the kid.' Things happen. We found out this was the kid God had in mind for us."
His wife, Ismary, has already decorated a room in their home in blue with a wallpaper border with baseball, soccer and football stickers.
"All the rooms at my house used to be pink with girls stuff," Zambrano said, happy to have another male in the house. "We have everything set up for him.
"It's a blessing," he said.