Genesis 6:4 says, "There
were giants in the
earth in those days; and
also after that, when the
sons of God came
in unto the
daughters of
men, and
they bare children to
them, the
same became mighty
men which were of
old, men of
renown." So there were giants in Noah's days when
the flood took place, and there were giants in the
days of Moses, Joshua, and David who slew the giant
Goliath which means some fallen angels came down a
second time and must have procreated with the
daughters of men a second time since every living
creature on earth was killed during the great flood
during Noah's time.
Genesis 6:17, "And, behold, I, even I, do bring a flood of waters upon the earth, to destroy all flesh, wherein is the breath of life, from under heaven; and every thing that is in the earth shall die."