Hello c,
Each of those child tracks have the ability to render the audio they carry; that means you can bounce at any track. Select the track you want to render and press B or define a segment in the arrangement with Punch In (I) Punch Out (O) and press Alt+B to render within a range.
Not sure if this advice helps but recording with an USB midi input is easy.
1. Select your track.
2. Pull out the menu from the input button and select your midi device.
3. Pull out the same menu again and select ‘Assign to focus track’.
4. Record Arm (R) the track and press K to begin recording.
Now clicking on any track will automatically map the midi input. This also works with audio inputs such as microphones.
Please refer to this page for further detailed instructions.