Al-Hasan and Al-Husayn would jump on his back and he, sallallaahu ‘alayhi wa sallam, would not get angry:

Under category: How He treated them?

Abu Hurayrah (a Companion) said: "We were praying 'Ishaa' behind the Prophet of Allah, sallallaahu 'alayhi wa sallam, and when he would prostrate Al-Hasan and Al-Husayn would jump on his back. When he raised his head, he gently moved them and put them on the ground. Then when he, sallallaahu ‘alayhi wa sallam, would go back down, they would climb on his back again, until he finished the prayer and sat them in his lap. I went to him and said: "O Messenger of Allah, I will return them." Then lightening struck in the sky, and the Prophet of Allah, sallallaahu 'alayhi wa sallam, told them: "You two go back to your mother." The light in the sky remained until they entered upon her."

Abu Bakrah (a Companion) narrated that the Prophet of Allah, sallallaahu 'alayhi wa sallam, was praying, and when he prostrated Al-Hasan would jump on his back and shoulders. The Prophet of Allah, sallallaahu 'alayhi wa sallam, would move him gently so that he would not fall over.

He did that more than once, so when he finished praying they asked him, "O Messenger of Allah, we saw you do something with Al-Hasan we have not seen you do before." The Prophet of Allah, sallallaahu 'alayhi wa sallam, replied

"He is my Rayhaan [a good smelling plant] in this life, and indeed this son of mine is a leader, and Allah will reconcile between two factions of Muslims because of him."

Thus, we see that the Prophet's dealings with his grandchildren were based on kindness and mercy, for a small child needs love and care from his parents just as he needs food and drink. This "emotional sustenance" is essential to raising a child with a balanced personality, free from complexes.