They are absolutely a human.
To sibling comment’s point: personhood versus humanity is already the legal distinction - eg, children and invalids are fully human but not fully people, so we don’t grant them full legal rights and instead let others exercise control over them. For children in particular, we grant them more autonomous control of their rights as they mature.
Your path of denying humans their humanity has a dark history, including within medicine.
I don’t support that, even if they’re very tiny and fragile humans early in their development — eg, if we could raise them in artificial wombs, they may have a right to life as a human, despite what anyone else wishes.
Denying their humanity is denying their right to life as a fellow human.