No. Each dependent qualifies in their own right — a legally married spouse or an unmarried child under 21 — and each carries a separate US$15,000 processing fee and US$1 million gift. Your newborn would be added as a dependent under the official instructions, not absorbed into your own principal package.
What the newborn has to satisfy in their own right
The relationship and the age condition are what make a child a qualifying dependent, and both are proved with documents rather than assumed from the principal's approval. The child must also be admissible and covered by an available visa, exactly as the rest of the household is. Follow the family instructions issued to your case for how the addition is made; do not assume a separate principal filing is required for every relative.
What any status permits is defined by the terms of that status, and the Gold Card program's terms are set out on its official government page. Bring the official instructions and the applicant's individual circumstances to a proper review. The official framework keeps eligibility for permanent residence, admissibility, vetting and visa availability as separate conditions.