Once the IRS receives your complete application via mail, you should receive an ITIN Assignment letter (on green paper) from the IRS with your ITIN usually within 7-14 weeks. Note that it can take longer during the tax season (January – April).
If the child isn't a U.S. citizen or resident, and if the child qualifies as a dependent, a TIN is still required. To obtain an ITIN, use Form W-7, Application for IRS Individual Taxpayer Identification Number. For more information, refer to Individual taxpayer identification number.
The paper application will take 4-6 weeks to process.
How long does it take? You will receive a letter from the IRS assigning your tax identification number usually within seven weeks if you qualify for an ITIN and your application is complete.
To avoid having to set up an ITIN in person, simply fill out this form to apply for an ITIN online right now. Sources: IRS. Individual Taxpayer Identification Numbers.