Two sheep sacrifice for a boy, one for a girl is a bida innovation in Islam that has no Qur'anic ruling.
It is a man made, pagan, idol worshipping practice that is termed a 'sunnah' by the lord and master maulana, mulla's, sheiks, mufti's etc etc so the rest of the sheep that are not sacrificed follow it deaf, dumb and blindly. Call anything a 'sunnah' and shirk becomes obsolete.
It is far,far, far better to feed the poor ALL YEAR ROUND and not bother with any child birth traditions; even feeding the poor at this time as all sacrifice is for and to Allah alone and any meat sacrificed for a child makes it haram.
6:145 Say, "I do not find in the revelation given to me, any food that is prohibited for one who wishes to eat, except: Carrion (dead meat), or running blood, or the flesh of swine – for it is unclean. Or, anything (not just meat) that, in defiance to commands, has been dedicated to other than God.” If one is forced by dire need without being deliberate and without transgressing, your Lord is Forgiving, Merciful. [2:173, 5:3. Rijs = Unclean = Disapproved = Contaminated = Foul = A barrier to moral development. Science still needs to learn how pork can be a barrier to morality. Fisq = Deviation = Abomination = In defiance of Divine Commands = Disobedience of God = Drifting away from reason]
Shirk = The act of being a Mushrik = Associating others with God = Accepting human authorities parallel to Divine revelation = Sectarianism = Idol worship in any form = Being content with manmade systems = Worshiping graves, saints, ancestors or one's own desire = Blind following or accepting religious information without discernment = Failing to use the Divine Word as the Criterion.