A US citizen can file an immigration petition for his parents only when the citizen is at least 21-year-old. So, your 4-month-old child would not be able to file any approveable petition for his father.
If you are eligible for US citizenship, you should apply for citizenship. There is no wait for a visa number for immediate relatives of US citizens. For immigration purposes, immediate relatives of a US citizen include a spouse, parents, and under-21, unmarried children.
If you are a green card holder, visa numbers are available for petitions with priority date of about September 2010.
You should review your specific facts with your attorney to find out your legal options.
You should re-post this question in the immigration forum.
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No. However, it will help if the permanent resident becomes a U.S. Citizen. Good luck.
This is general information, not legal advice, and does not create an attorney client relationship.