The 1979 version…

Even Ron Scribner himself doesn't know why. Granted, he was only 13 during filming, but he'd know if anyone. He chalks it up to a wardrobe error. And Tobe Hopper doesn't clarify any of our questions about this film in his director commentary. I watch a lot of movie commentaries, and his was the worst I've ever come across. Anyways, 2 of my theories are that the pajamas in and of themselves are facade that Ralphie was putting on while he was trying to mesmerize his brother into opening the window. Since it was night time, and nighttime means jammies, then maybe the thought of Danny seeing his brother in pajamas at night would persuade him more to open the window for him. Just like at the end of the film when Susan is all dolled up in her glamorous gown and makeup and hairstyle, I believe that could have been a facade also that she was using to try to mesmerize Ben into letting her bite him. My other theory is, if you read the book, Ralphie's clothes are found in the basement of the Marsten house. Which would indicate that Straker removed his clothes for some reason. Now since in the book Ralphie does not turn into a vampire or float outside anybody's window, he was simply a sacrifice that Straker made to Barlow. So maybe putting the pajamas on ralphie was Toby Hooper's way of giving a nod towards that aspect of the book. A nod to how Ralphie's clothes were found in the basement. And then when Ralphie shows up at the end of the movie slumbering In the root cellar back in his street clothes that's either because his pajamas was a facade he was putting on for his brother Danny, or, that was the wardrobe malfunction by Toby Hooper. It's just one of the many questions that plague us hardcore Salem's Lot fans over the years.