CARRIE UNDERWOOD and her husband, hockey stud MIKE FISHER, are expecting their first child. 

She posted an Instagram yesterday of her two dogs wearing shirts: One read, "I'm going to be a big brother" . . . and the other said, "I'm going to be a big sister."


She captioned it: Quote, "In honor of 'Labor' Day, Ace and Penny would like to make an announcement. Their parents couldn't be happier." Carrie's people also confirmed the pregnancy, and that she's due in the spring.


Mike got into the act by joking about it with a post on Twitter. That one read, "We haven't picked names yet but it's looking like Fly is going to fly." He hashtagged it "FlyFisher." 


Would Carrie REALLY let him name their youngin FLY FISHER?