Saying #1: "This is the pumpkin, orange and bright, that sits on the sill and grins at the night,"
Inference : I think that maybe the the pumpkin has been carved into a huge grin and the pumpkin is bright because he could have a light in it.
Inference: Image #1- The kid's are trick-or-treating on Halloween because they have costumes on and the people in the house are holding a bowl.
Saying #2: "This is the principal, wild as west. Twirling his lasso, a star on his vest." Inference #2 : Maybe the principal is dressed up as a cowboy.
Inference: Image #2- I think that the kid's have gotten home and put on their pajamas. It look's as if they're now laying on the floor separating their candy and eating it.
Saying #3: "This is the costume, ghastly and green, that Max and his mom made for Halloween." Inference #3: Maybe the boy/girl is dressed as a green monster or creature. He could be dress as a tree or bush also.
Inference: Image 3- I think that kid's are about to get on the van, and go off to a Halloween party because they all have costumes on.