From the benefits of having children is that if they were to pass away whilst still children, they will intercede for their parents. This is authentically reported from the Prophet (s), who said: "There is no Muslim individual, male or female, who has three of his children pass away whilst they are young and he is patient with that, except that they will come and intercede for him on the Day of Judgment." So 'Umar (r) asked, 'what about two [children]?' Upon this the Prophet (s) said, "It is the same for two [children]." (Al-Bazzaar, al-Haakim. Sh. al-Albaanee mentions it in his book, Kitaabul-Janaa-iz)  As for the person who has one child who passes away and he is patient with this, seeking his reward from Allah (S), then he shall also find a great reward with Him. As in a hadeeth wherein it is reported that the Prophet (s) used to sit down in his sitting place and his companions would sit in front of him to seek benefit and learn from him.

From amongst them was a man who had a small boy; he used to come to the Prophet (s) from behind his back by way of respect, then he used to sit in front of him and sit his son in front of the Prophet (s). The Prophet (s) asked, "Do you love this child of yours?" The man replied, "Yes, and may Allah cause you to love him also." Then it happened that this child passed away, and the man was so sad that he used to refrain from coming to sit with the Prophet (s). So the Prophet (s) asked his companions about this man saying, "Why is it that he no longer comes to my sitting place?" This was from the Sunnah of the Prophet (s), that if he had people who would come to him and then stop coming, he would ask about their condition and their affairs. So the companions told him that the man's son had passed away and that he was sad because of that. The Prophet (s) went to see this man and asked him, "What has happened to your son?" And the man told him that he had passed away. So the Prophet (s) said, "Do you wish that your son could be here with you spending time with you, or do you prefer that your son would reach Paradise before you, waiting at the Doors of Paradise to open them for you?" So the man said, "O Messenger of Allah. I wish that my son would go forth before me and precede me to Paradise." So the Prophet (s) said to him, "Verily, this is for you." So upon this, one of the companions said, "O Messenger of Allah, may I be sacrificed for your sake! Is this (reward) only for this man or is it for all of the people?" He (s) said, "No, this reward is for all of the people (i.e. those who lose a child and are patient with their loss)." (Al-Haakim. Adh-Dhahabee declared it Saheeh as did Sh. Al-Albaanee)