Please God, DON'T.

If you even start getting people to treat the alto recorder as a transposing instrument you will set them up for years of confusion.

Recorders DO NOT TRANSPOSE. Never have done. Take a part in a recorder group and you will never be offered transposed alto recorder music. Whether for mediaeval, baroque or contemporary music, you can't buy transposed alto recorder scores. Everything is published at pitch.

It takes most people about two weeks to learn to sightread using F alto fingerings if they're accustomed to doing it on the C descant. Just put the C recorder away and only play the F while you're making the transition. Another couple of weeks and you'll be able to switch between them fluently.