@Strannger18 said:

I was thinking that since vampires need an invitation to enter a residence that the windows being opened was an invite itself. It would explain why they didn't come in themselfs, but needed a victim to willingly do it themselves

According to my understanding of the folklore, a specific invitation has to happen, otherwise, it's no-go.

On the IMDb board, various silly explanations were offered for Barlow's entrance into the Petrie house, such as his alleged status as a 'master' vampire, which does not exist in the relevant folklore, to his entrance into the town being invitation enough, to the house itself inviting him in, but the simplest and most logical explanation is that King (and the subsequent screenwriters) goofed.