learning to recognize the intervals...
would be essential...

the most common example of a third
might be the ding dong of a door bell

Do, a deer, a female deer, might also
have some good examples...

it is good if the singer can tell what
note to sing when it is written...that
is probably the best way to start...

good luck.

your experience with church and school
choirs must give you a good background
many musicians got their start in church