He, sallallaahu 'alayhi wa sallam, would hold them on his shoulders:

Under category: How He treated them?

Abu Hurayrah narrated that the Prophet of Allah, sallallaahu 'alayhi wa sallam, came out carrying Al-Hasan and Al-Husayn on each shoulder, and he, sallallaahu ‘alayhi wa sallam, would kiss each one of them. When he reached the people, a man remarked to him, "O Messenger of Allah, you love them!" The Prophet of Allah, sallallaahu 'alayhi wa sallam, replied: "Whoever loves them, then he loves me, and whoever hates them hates me.

If we were to compare the state of the Prophet of Allah, sallallaahu 'alayhi wa sallam, with his grandchildren to ourselves, we would discover the difference of attitude, as many people nowadays have abandoned raising and playing with their children and left them with servants, nannies or babysitters. Thus, the child grows up in the care of this "imitation mother" and he does not experience any love from his real parents.