If your gifts to your son exceed $15,000 in total during the year, you (the donor) may have to file a gift tax return, IRS Form 709. This is a required form for reporting purposes. Actual gift tax is not due until the lifetime amount exceeds $11.18 million.
For more details, see Who Must File on page 2 of this reference: https://www.irs.gov/pub/irs-pdf/i709.pdf
Note that your spouse may also gift $15,000 or less without a reporting requirement, so that the two of you may gift $30,000 in total without having to file Form 709.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
