That Phase.......

Some of you know exactly what I'm talking about. My son, soon to be 6, has entered the stage in his life where he thinks everything is cool. Even when it isn't. He comes up with some of the goofiest scenarios. I know it is great that he is thinking about cause and effect. Sometimes I don't really know how to respond without shooting him down. For instance, he will say something like, "Hey Mommy, what if lalalalalala blahblahblah lalalalala." and then I am like " Well, then lalalalalala blahblahblah lalalalalala." Catch my drift? Anyway, I'm praying that some of this calms down when he starts kindergarten. I love my son and his imagination. Sometimes I love them separately. So I am asking for input from any of you Moms of grade school children. Where do I go with this?