Srimad Bhagavatam Canto 10, Chapter 18, Text 13

SB 10.18.13

kvacin nrtyatsu canyesu
 gayakau vadakau svayam
sasamsatur maha-raja
 sadhu sadhv iti vadinau
 
Translation: 
 
While the other boys were dancing, O King, Krsna and Balarama would sometimes accompany them with song and instrumental music, and sometimes the two Lords would praise the boys, saying, “Very good! Very good!”
Srimad Bhagavatam Canto 10, Chapter 18, Text 12
Srimad Bhagavatam Canto 10, Chapter 18, Text 14