Tanchuma Kedoshim 14: In this world, the Yetzer ha'Ra is found among you; you sin, and your children die. In the future, I will remove the Yetzer ha'Ra from among you; you will beget and rejoice, "Ki Zera Beruchei Hashem Hemah v'Tze'etza'eihem Itam."

Radak: This is the opposite of the curse "u'Zratem la'Rik Zar'achem v'Achaluhu Oyveichem" (Vayikra 26:16). All their toil will be for a Brachah. Neither enemies, Shidafon nor Yerakon (parched by the east-wind, and dried and turned straw-yellow - Rashi Devarim 28:22) will consume their toil.

Malbim: They will not plant and others will eat it.

Radak, Malbim: Children will not die in their parents' lifetimes; parents are befuddled over death of their children.

Mishnah Berurah (47:10): Parents should always pray that their children learn Torah, and be Tzadikim with good Midos. They should have special intent for this in Ahavah Rabah, Birkas ha'Torah and when saying l'Ma'an Lo Niga la'Rik v'Lo Neled la'Behalah in u'Va l'Tziyon.

Malbim: This corresponds to Lo Yig'u la'Rik - they are blessed, and will outlive the work of their hands.

Radak: All their days, [their children will not die; they] will be with them. The matter is repeated in different words. Malbim - until now, all this explains why crying will not be heard.