It's all part of the human life cycle which begins at conception and ends at death. Every stage along that continuum is fully human with the appropriate attributes for that particular stage of the continuum.
"An individual human life begins at conception when a sperm cell from the father fuses with an egg cell from the mother, to form a new cell, the zygote, the first embryonic stage. The zygote grows and divides into two daughter cells, each of which grows and divides into two grand-daughter cells, and this cell growth/division process continues on, over and over again. The zygote is the start of a biological continuum that automatically grows and develops, passing gradually and sequentially through the stages we call foetus, baby, child, adult, old person and ending eventually in death. The full genetic instructions to guide the development of the continuum, in interaction with its environment, are present in the zygote. Every stage along the continuum is biologically human and each point along the continuum has the full human properties appropriate to that point."
Dr. William Reville, University College Cork, Ireland