The family will welcome their third child in May, his rep confirms to PEOPLE. The new addition joins big brothers Rhys Edward, 1, and Griffin Thomas, 3.
"Barrett and I are so blessed and grateful for the little one on the way," says McIntyre, 37. "We'll have our hands full. Three's the new nine!"
The New Kids on the Block singer, one of nine children himself, wed Barrett in Aug. 2003 at New York City's Plaza Hotel.
Reporting by MICHELLE TAN