Delta. I actually found the information when going through the listing process.

So technically yes, but it may be a hassle with the way i'm booking them. I have to list the kids together (without me) for the full IND-ATL-TPA flight, which then no longer appears as a non-stop domestic.
I guess I'll fly with them to the destination and return the following day.

Between 5 and 14 years of age
 May travel unaccompanied on non-stop domestic flights only (includes Canada and the Caribbean).

May not travel unaccompanied on any international flight, including flights to Mexico, Central America or South America.

Delta accompaniment services are not available to nonrevenue/reduced rate passengers and no service charge will be collected. However, the Unaccompanied Minor Envelope must be completed at check-in. This documentation ensures that the child is escorted to the gate and met in the final destination by a designated adult.

 Not permitted to travel on nonstop domestic red-eye flights greater than two (2) hours in duration departing between 9 pm - 5 am. This additional restriction does not apply to nonstop flights to/from Alaska and Hawaii, or nonstop flights in markets which only have a single daily flight and that flight is a red-eye flight (i.e. LAX-FLL, SJC-ATL, etc.).
Age 15 - 17
 ​May travel unaccompanied on all flights. Any minors (15-17) traveling with another minor (5-14) will be included in the UMNR program and the rules which apply to the youngest child will apply to all children.