This song is a favorite of Shabana Azmi. She rightly says that it is indeed a genius mind of Kaifi azmi at work here. It is easy to express sad emotions with serious lyrics but to express the heartfelt pain of Shanti in separating from Suresh Sinha in a kid's rhyme is indeed marvellous and lyrics composing at its best.
KAIFI AZMI (Athar Hussain Rizvi, hails from a small village called Mijwan, near Azamgarh, Uttar Pradesh)
Guru Dutt considered Khyaam for the music but later Burman accepted. as S.D. burman and sahir never wanted to work together again after pyaasa as well as Sahir was not in good terms with Guru dutt, Kaifi azmi was given the task by Guru Dutt himself.
Bappa this is also one of my favourite Songs...Specially the Children Singing in chorus( Ek do teen ...Chaar aur panch..).