I am currently expecting a second bundle of joy, and my sister in law bought this for my 3 year old to explain to her where babies come from.
This is a hilarious book, it explains how babies are made, and yes, this does include the fact that the act of love making does need to occur. However this is dealt with in a fun and inoffensive way. If people honestly think that this will encourage children to try it out for themselves, I say go ahead, let them try, it will be safer than contraception as there is no way I can work out how to make love whilst tied up with helium balloons!
My 3 year old is happy with the explanation, and like the other reviewer, believes the baby comes from the bottom and has asked no further questions. This is a good, light hearted way to give children the basics correctly which can be developed when the time comes for the next stage of the `birds and the bees'.