"Trying to get back into #boyband shape with my little buddy for our next #backstreetboys album and tour," Carter posted to Instagram, along with an adorable shot of himself with his 4-month-old bundle of joy. "Pushing a stroller is crazy cardio lol."
Carter clearly can't get enough of his little boy.
"I do not mind at all changing diapers," he told ET in May about how he's handling daddy duty, before admitting he’s still got some learning to do. "I don't think [Lauren] wants me to change them as much because I am not as good as her in that."