There was a little girl and her mother walking through the
park one day and they saw two teenagers having sex on a bench.

The little girl says "Mummy what are they doing?".

The mother hesitates then quickly replies "Ummm they are
making cakes". The next day they are at a zoo and the little girl
sees two monkeys having sex. Again she asks her mother what
they are doing and her mother replies with the same
response, making cakes. 

The next day the girl says to her mother
"Mummy, you and Daddy were making cakes in the lounge last
night eh?". Shocked, the Mother says "how do you know?"

She says, "Because I licked the icing off the sofa".