"Making Cakes" joke

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.''

Shocked, the Mother says' 'how do you know?''

The little girl replies,' 'I licked the icing off the sofa.''