When Winston goes to Mrs Parson apartment ,the children blame him as threater ?wohat is the reason or thing that they define him as threater ?

There is really nothing that marks out Winston as a traitor to the party. The Parson Kids are just bored, aggressive, and paranoid. They have been taught by the party to be weary of adults as potential "spies" to the state. Winston was conveniently there on a day they were bored and wanted to see violence.