I am just elated. My 15-month-old surprised me by singing ACBD with the correct rhythm and sounds which definitely sounded like the alphabets. He sang till alphabet K with the correct rhythm, after which he sings his own tune. To comfirm, I asked him to sing it 6 or 7 times the whole day, and each time he was able to sing until K. Two weeks back, he sang bah bah black sheep by just saying ba ba ba ba in the exact rhythm till "have you any wool." He hasn't started talking as yet. He says quite a few two-syllable words. So I am actually surprised he is able to vocalize the alphabets with the correct tune.