How many baby boys were killed when Pharaoh was trying to kill baby Moses?

Egypt occupies a very large territory and any instruction to kill Hebrew babies would have to have been put in writing and distributed throughout the land, but no such written instruction has ever actually been found in Egypt, and in fact there is no record that even hints of the presence of the Israelites there, so we must rely on the biblical account. The Bible says that the pharaoh ordered all the new-born Israelite boys to be cast into the river.

Since Moses lived to be 120 years old, he must have already been 80 years old when he led the Israelites out of Egypt. And we know that the Bible attributes his survival to the pharaohs daughter. This passage implicitly assures us that, apart from Moses, there could scarcely have been any Israelite males under eighty years old, although other passages do seem to contradict this.