"Making cakes" joke

A mother and daughter were walking through the park one sunny afternoon. They passed a bench where two teenagers were making out. The daughter turns to her mother and asks
"What are they doing?"
The mother stutters and replies
"They are making cakes dear"
The next day the mother took the daughter to the zoo. They went to see the gorillas. When they got there the gorillas were shagging in the cage. Again the daughter turns to the mother and asks
"What are they doing?"
The mother is not as shocked and remembers what she had said to her daughter in the park.
"They are making cakes dear"
That night the mother and father got jiggy on the sofa. The next morning the daughter comes into the kitchen and asks her mother
"Mum, were you and dad making cakes on the sofa last night?"
The mother was very embarrassed and turn to her daughter and said
"Why dear?"
To that the daughter replied
"Because i just licked the icing off of the sofa"