How did the sorcerers know about the birth of the Prophet Moses (peace be upon him), given that knowledge of the unseen belongs to Allah the Almighty?

The sorcerers were unaware of Moses' birth; it was Pharaoh who knew about it. This knowledge came to him either through a traditional prophecy attributed to Abraham (peace be upon him) stating that the destruction of the king of Egypt would be at the hands of a boy from Abraham’s descendants, or through a dream Pharaoh had, which was interpreted for him to mean that his demise would be at the hands of a boy born among the Children of Israel.