Bhagavatapurana 2.3.15

2.3.15

sa vai bhāgavato rājā pāṇḍaveyo mahārathaḥ /
bālakrīḍanakaiḥ krīḍan kṛṣṇakrīḍāṃ ya ādade //

15. That great warrior of the Pandava race was a well-known devotee of the Lord (Sri Hari); (for), playing with toys, while ye a child, he made the worship of Sri Krishna one of his plays.