"Being able to hold and cuddle and have a little baby cuddle against you and fall asleep is such a fleeting moment in time, and I really can't wait for that again," the Entertainment Tonight correspondent, 36, tells PEOPLE.
This will be the second child for the former Dancing with the Stars co-host and husband Michael Hess.
The couple welcomed daughter Josselyn Sydney Hess in September 2007.
"I'm most excited to have a second child to play with Josselyn, to see how Josselyn blossoms as a young girl being able to teach a sibling all that she knows," says Harris. "She's so excited. She tells me every day the different things she's gonna teach the new baby."