"The Easter Bunny brought a very special egg this year!" Richardson, 41, tweeted on Sunday.
This news comes ahead of the Backstreet Boys' 20th anniversary concert set for April 20 and marks the second child for the happy couple who welcomed son Mason in July 2007.
The newest addition to the Richardson family will have no shortage of playmates, as two other BSB members have announced baby news within the past year. Howie Dorough welcomed a son in February while A.J. McLean welcomed a daughter in November.