The grand sire will certainly not want to kill them. But Karna is the Pandavas' chief enemy.

He is anxious to please, Duryodhana by killing my sons. Karna is a great man-at- arms. As I think of him engaged in battle against my other sons, my heart is consumed with agony like a faggot in the fire.

Now is the time for me, to seek Karna out and tell him the truth about his birth, on knowing which, he is bound to abandon Duryodhana's cause."

Tormented by these anxious thoughts about her children. Kunti went to the banks of the Ganga where Karna usually offered his daily prayers.

Karna was there at his devotions. Facing  east and with uplifted hands he was in deep meditations. Kunti quietly stood behind him and waited.

Karna was in meditation and was unmindful of everything until he felt the, hot rays of the sun on his back.