Jack is absolutely right. DO NOT TRANSPOSE Music for C recorders so that F recorders can read as if they were transposing instruments. The recorder is never written as a transposing instrument and if he wants to learn an F instrument he must learn to read it at pitch. True it lets you get started quickly but your friend will pay the price for it in the long run. All recorder players need to learn to read and play both C and F instruments at pitch. It's not that difficult it just takes a bit of adjusting - and, of course, practice. The fingerings are actually the same, it's just that they produce different notes and you have to learn that.

If he wants to play Bass recorder, then he must, repeat, must learn to read in bass clef because bass recorder music is always written in bass clef.

When I started playing bass recorder, I got a selection of tunes that I knew well and transposed them to the bass clef, so I could read them at pitch but using the bass clef and then I worked through them. Because I knew the tunes well, it meant I could concentrate on reading in the bass clef and learning the fingerings. It took about a week to adapt. I find it easier to transfer between soprano or tenor and bass than I do to between soprano or tenor and alto.