If one’s son has died, one may certainly be affected by lamentation and illusion and cry for the dead son, but one may overcome lamentation and illusion by considering the verses of Bhagavad-gītā.

jātasya hi dhruvo mṛtyur dhruvaṁ janma mṛtasya ca

As the soul transmigrates, one who has taken birth must give up the present body, and then he must certainly accept another body. This should be no cause for lamentation. Therefore Lord Kṛṣṇa says, dhīras tatra na muhyati: one who is dhīra, or sober, who is learned in philosophy and established in knowledge, cannot be unhappy over the transmigration of the soul.