Aslam o alikum 1st q, that a new born baby in a nonmuslim family,is a by birth muslim or masoom ? 2nd q , if any nonmuslim accept islam what shall we call him in english convert or revert? 3rd q , when exectly islam started in the world?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

The Prophet informed us that every child is born on the Fitrah (human natural disposition to worship Allaah alone); this means that he is free from wrong beliefs and is prepared to accept the truth and correct belief. The Fitrah does not mean that the people embrace Islam and adhere to its rulings from birth.

Ibn Taymiyyah said: "Being born on the Fitrah does not necessarily mean that one really believes in Islam at birth, because when Allaah brought us to this life (at birth) we do not know anything. Fitrah refers to having a pure heart which is ready to accept the truth, and that a person would be a Muslim if no one influenced him (while growing up) to change his natural inclination towards Islam."  A new-born child to non-Muslim parents is in reality born upon the Fitrah, which means that he is free from wrong beliefs and is prepared to accept the truth; if his parents do not spoil him with falsehood, he can only be a Muslim. Concerning religious rulings, the child follows (i.e. is traced back) to the best among the two parents in terms of religion.

Therefore, we know that whoever embraces Islam after disbelief, is a revert. As regards your last question, Islam in the broad concept of worshipping Allaah Alone started from the time of the Prophet Aadam he was a Muslim and all the Prophets and Messengers, may Allaah exalt their mention, were Muslims as we mentioned in Fatwa 88906. Therefore, Islam is the origin and Shirk (associating partners with Allaah), is an innovation. Allaah Says (what means): {Indeed, the religion in the sight of Allaah is Islam.}[Quran 3:19].

However, Islam in the special sense, which is the legislation that was revealed to Muhammad started when the Prophet was commissioned a Prophet and Messenger. For more benefit please refer to Fatwa ">85767.    

Allaah Knows best.