"Stick Together" joke

Fred and Mary get married but can't afford a honeymoon, so they go back to mom and dad's for the night. In the morning, little Johnny gets up and has his breakfast. As he is going out of the door to go to school, he asks his mom if Fred and Mary
are up yet.
She replies, "No".
Johnny asks, "Do you know what I think?"
His mom replies, "Never mind what you think! Just go to school."
Johnny comes home for lunch and asks his mom, "Is Fred and Mary up yet?"
She replies, "No."
Johnny says, "Do you know what I think?"
His mom replies, "Never mind what you think! Eat your lunch and go back to school."
After school, he comes home and asks, "Is Fred and Mary up yet?"
His mom says, "No."
Johnny asks, "Do you know what I think?"
His mom replies, "OK! What do you think?"
He says, "Well, last night Fred came in for the Vaseline and I think I gave him my airplane glue."