So, now that we have taught them where all the Cs are, let us teach where middle C is. Now, in the center of the piano where the pianist always sits and you see the brand of the piano, the label is there. Next to that two black notes on your left, this is white note is middle C. Listen to that, that is middle C.
Now, a good little exercise for them to practice and at the same time learn middle C is to curve the hand and keep the fifth finger tucked under the hand. Now, using the third finger play middle C, then the second finger, then the thumb 3-2-1-3-2-1, and same thing with the left hand 3-2-1-3-2-1.
Now, let them practice that and repeat this little exercise and little sessions until they can do it and get some facility doing it 3-2-1-3-2-1-3-2-1 and then do the opposite 1-2-3-1-2-3-1-2-3-1-2-3-1-2-3 and then alternating the hands later on and they become more expert 3-2-1-3-2-1-1-2-3-1-2-3-1-2-3-1-2-3-3-2-1-1-2-3.
Be imaginative and with time you will see you will get a nice little technique prime like that. This great little exercise, it prepares them for scales later on. Remember, do not expect them to learn everything right away. Take your time and have them relaxed and enjoy the lessons.