Do you believe that a newborn baby is fully human? Answer: Yes.
The answer depends on what you contextually mean by “human”. If by “fully human” you mean “member of the species Homo sapiens sapiens, with a full corresponding complement of chromosomal DNA” then the answer is “yes”.
But then you are limited only to the inferences you can draw from that definition. For instance, a corpse is fully human by that definition, so if you want to exclude corpses, you have to alter the definition, by specifying “a living organism” instead of just “a member.”
In what sense is a newborn baby not fully human? There is at least one general sense: newborn babies are not developed to full and normal human potential. So if by “fully human” you mean “fully developed human” then the answer to the question is “no.”
Do you believe that a newborn baby is a person? Answer: Yes.
I do not believe babies are fully developed persons, but I do believe they are persons. Babies become persons before birth, at the formation and activation of their cerebral cortex (around the start of the third trimester, although the exact timing differ in each individual case). Babies have all the attributed of personhood; they only possess them in lesser degree than older children, who in turn possess them in lesser degree than adults.
These answers are based on the answers given by historian and philosopher Richard Carrier to the same questions HERE.