Party Favor - S2-E13
Visible crew/equipment: When Doug goes back to the house after unsuccessfully scraping the frost off the car, a stage light is reflected in the window to the right of the front door. As Doug approaches the door his own shadow passes over this reflection. (00:01:30)
Party Favor - S2-E13
Visible crew/equipment: When Doug and Carrie are arguing about Danny coming over, you can see a stage light (not on) through the door window. We can also the neighbours garage, which we know from many outside shots of the Heffernan's backyard, is not that close to the house. (00:01:50)
Frozen Pop - S2-E15
Visible crew/equipment: At the very beginning, when Carrie walks in, a boom mic is visible above her. It then quickly moves out of shot. (00:00:05)
Frozen Pop - S2-E15
Visible crew/equipment: When Doug goes to scrape the car, a stage light is reflected in the iced up windows. (00:01:05)
Frozen Pop - S2-E15
Visible crew/equipment: When Doug is scraping the car, watch carefully and you can the the reflection of someone off screen behind the camera move. (00:01:10)
Frozen Pop - S2-E15
Visible crew/equipment: While Doug is scraping the windshield in the wide shots, the end of the street backdrop and production equipment are visible at the upper left side of the screen. (00:01:15)
Frozen Pop - S2-E15
Visible crew/equipment: When Arthur puts his big red jacket on and goes downstairs, Carrie follows and tape markers are visible on the floor by the door. (00:16:30)
Visible crew/equipment: When the group enters the house at the start, there are a few little white dots strategically placed on the floor where actors stop. Clearly place markers. (00:02:00)
Visible crew/equipment: When Doug mentions about a mistake in the word jumble, look in the glass above him to see a boom mic reflection clear as day. (00:01:45)
Visible crew/equipment: When Arthur is hinting it's his birthday soon, there is one shot where you can see the cupboards above the hatch into the kitchen. In this shot you can see a boom mic follow Arthur across the room. (00:02:30)
Visible crew/equipment: When Arthur walks into the living room humming the Happy Birthday tune, as he bends down to pick up the magazine, a camera is visible on the right side of the screen. (00:02:30)
Visible crew/equipment: When Doug is sitting in the living room and Carrie comes into the kitchen carrying groceries, a boom mic shadow is seen moving on the wall behind her. (00:04:10)
Visible crew/equipment: After Doug gets Arthur out of the house he takes him to a restaurant, and as they both take their seats, the two sets of double tape marks are visible on the carpet under the table. Then, when Doug stands up another small tape mark is visible at his feet. (00:06:30 - 00:08:00)
Visible crew/equipment: When Doug and Arthur are eating in the buffet restaurant, stage lights are seen reflecting in the cup. Also, each time the camera goes from angle to angle, the cup has moved from one side of the table to the other, sometimes have a saucer, sometimes not. (00:06:35 - 00:08:20)
Visible crew/equipment: When Carrie and Arthur pull into the driveway, the camera is reflected in the car. (00:18:15)
Soft Touch - S2-E22
Visible crew/equipment: At the start, in the shots facing Carrie and Doug while they're in the car, we can see a screen atop the roof on the driver's side of the car with its reflection on the windshield (and its shadow on the car's hood). This is gone in the overhead long shots. (00:00:10)
Soft Touch - S2-E22
Visible crew/equipment: When Doug and Carrie go to get up from having dinner with Saskies, tape markers are visible on the floor by their chairs. (00:05:30)
Soft Touch - S2-E22
Visible crew/equipment: When Doug gets into bed after arguing with his cousin, a camera shadow can be seen moving over the bed. (00:17:45)
Visible crew/equipment: When Carrie says about going back in time, a boom shadow can be seen moving over the wall. (00:02:30)
Visible crew/equipment: Lighting equipment is visible in the lower left corner of the shot of the outside of the Heffernan home. (00:14:42)
Answer: To answer the question directly. Carrie and Doug do not have a biological child during the show's main run. In season 3 or 4 finale (cant remember which) Carrie has a miscarriage. Later on in the show they find out Carrie has 1 working ovary. Thus reducing the chance of them conceiving. By the final season, they couple agree to adopt from China and go to collect their child in the show's final episode. While on the flight back from China it's revealed that Carrie is once again pregnant. However the last scene of the show is a flash forward showing that Carrie goes full term with that child and they are struggling with both kids.
Ssiscool ★
Adding on to this answer, I read somewhere that producers were afraid of the show having a "before baby" feeling and then an "after baby" feeling. Some fans feel that main characters, or the show in general, decline in quality after a major change. For example, Jesse and Rebecca on "Full House" after they had twin sons, and Daphne on "Frasier" after she married Niles.