SB 10.7.7
adhah-sayanasya sisor ano ’lpaka-
pravala-mrdv-anghri-hatam vyavartata
vidhvasta-nana-rasa-kupya-bhajanam
vyatyasta-cakraksa-vibhinna-kubaram
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Lord Sri Krsna was lying down underneath the handcart in one corner of the courtyard, and although His little legs were as soft as leaves, when He struck the cart with His legs, it turned over violently and collapsed. The wheels separated from the axle, the hubs and spokes fell apart, and the pole of the handcart broke. On the cart there were many little utensils made of various metals, and all of them scattered hither and thither.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Srila Visvanatha Cakravarti Thakura has commented on this verse as follows. When Lord Krsna was of a very tender age, His hands and legs resembled soft new leaves, yet simply by touching the handcart with His legs, He made the cart fall to pieces. It was quite possible for Him to act in this way and yet not exert Himself very much. The Lord in His Vamana avatara had to extend His foot to the greatest height to penetrate the covering of the universe, and when the Lord killed the gigantic demon Hiranyakasipu, He had to assume the special bodily feature of Nrsimhadeva. But in His Krsna avatara, the Lord did not need to exert such energy. Therefore, krsnas tu bhagavan svayam: Krsna is the Supreme Personality of Godhead Himself. In other incarnations, the Lord had to exert some energy according to the time and circumstances, but in this form He exhibited unlimited potency. Thus the handcart collapsed, its joints broken, and all the metal pots and utensils scattered.
The Vaisnava-tosani remarks that although the handcart was higher than the child, the child could easily touch the wheel of the cart, and this was sufficient to send the demon down to the earth. The Lord simultaneously pushed the demon to the earth and superficially broke the handcart.