You can file Form I-130, that's alien relative petition, for your child under the F2A category, which is for spouses and unmarried children under 21 of green card holders. Once the petition is approved and a visa becomes available, your child can apply for an immigrant visa.

The F2A category usually has shorter wait times than other family categories, but you should still monitor the Visa Bulletin each month to track when your child’s priority date becomes current.

Make sure your child has a valid birth certificate and passport, and be prepared to show evidence of your relationship when the case reaches the consular processing stage. Attending the visa interview prepared can help avoid delays.