I rent a house to my children for below fair market value. They pay principal and interest and I pay escrow. How do I report this?

This is a not-for-profit rental.

Not Rented for Profit

If you don’t rent your property to make a profit, you can’t deduct rental expenses in excess of the amount of your rental income. You can’t deduct a loss or carry forward to the next year any rental expenses that are more than your rental income for the year.

Where to report.

 Report your not-for-profit rental income on Schedule 1 (Form 1040), line 8. If you itemize your deductions, include your mortgage interest and mortgage insurance premiums (if you use the property as your main home or second home), real estate taxes, and casualty losses from your not-for-profit rental activity when figuring the amount you can deduct on Schedule A.