Ganesh

Lord Ganesh has been worshiped by allmost all the Hindues. He is the 'elephant head god ' for those who are not familial with the hindu mythology. He is the son of Lord  Shiva and Parwati . The story of his birth and of his elephant head does not make sense as are many mythological stories in Hinduism. Parwati wanted to take shower  and needed someone to guard, on lookout for enemies. So she created Ganesh from the body 'mal' -dirt. While she took shower , Lord Shiva came in . Genesh would not allow him to go in . Lord Shiva cut off the head of Ganesh. When Parwati came out and found this she was upset and ask Shiva to correct his mistake . So Shiwa's Gana went out and got head of the 1st animal they saw --happened to be an elephant and brought it . Then Lord Shiva attached it to the ganesha's body . Now the questions arise . Why did Shiva not recognise his son Ganesh? Why did he not attach Ganesha's head that he had chopped off and look for the new one ? Is killing child ( balhattya ), and killing elephant --not major sins ? Certainly there are no valid reasons that one could have.