Carrie was pregent with Mitchell. In episode 4 Marshall wanted to know if it was a boy or a girl so he was going to use one of op-tech for one of Sydney's trips. In the episode called "After Six", Carrie was going into larbor and Mitchell was born. In Blowback Marshall was showing pictures of Mitchell to Sydney, Vaughn, Weiss, and Laruen. When the befling was starting Marshall showed Jack a picture too.
In The episode called Tuesday, Marshall was leaving to go to work and his Kid Mitchell was sick and Carrie might have taken him to the doctor but it was never shown. At the end of the episode Sydney drops off Marshall and Marshall sees Carrie and Carrie.
In the episode called "Reprisal", Mitchell says the word Daddy and Marshall goes and sees what's up. After that Carrie goes and sees what's up. Marshall is kidnapped by Sloane follow by Rachel too. Carrie calls Sydney and Jack and then Carrie says Mitchell is at her mother's house. Marshall is later safed by Sydney, Vaughn, Dixon and Tom. In The Series Final Dixon vists Sydney and Vaughn and tell Carrie is stuck on bedrest and that's 4 brother of Mitchell.