Du’a for Sick Child
Question

What du`a should a parent say for a child who is sick?
Praise be to Allah.Du’a for sick child
The Prophet (peace and blessings of Allah be upon him) has taught us things in such cases in which there is healing and a lessening of sickness, as well as reward. That is part of Allah’s mercy towards this blessed ummah and the Prophet’s care for it. He is the one whom Allah described as (interpretation of the meaning): 
“Verily, there has come unto you a Messenger (Muhammad (peace and blessings of Allah be upon him)) from amongst yourselves. It grieves him that you should receive any injury or difficulty. He (Muhammad (peace and blessings of Allah be upon him)) is anxious over you; for the believers (he is) full of pity, kind, and merciful.” [al-Tawbah 9:128]
Among the things that he taught us are the following: 
·        Reciting al-Fatihah 
Abu Sa’id al-Khudri (may Allah be pleased with him) narrated that the Prophet (peace and blessings of Allah be upon him) described Surat al-Fatihah as a ruqyah, and he approved of the Sahabi who recited it as a ruqyah for the one who had been stung by a scorpion. (Al-Bukhari (2156) and Muslim (2201)
Ibn al-Qayyim said: 
“There was a time when I fell sick in Makkah, and I could not find a doctor or any medicine, so I treated myself by reciting it. I would take some Zamzam water and recite it over it several times, then drink it. I recovered fully by these means, then I began to do that whenever I felt a lot of pain, and I benefited greatly from it.” (Zad al-Ma’ad, 4/164)
·        ‘Aishah (may Allah be pleased with her) narrated that when any of us fell sick, the Messenger of Allah (peace and blessings of Allah be upon him) would wipe him with his right hand then say: “Adhhib il-bas, Rabbi l-nas washfi anta al-Shafi la shifa a illa shifa uka shifa an la yughadir saqaman (Remove the harm, O Lord of mankind and heal him, for You are the Healer and there is no healing except Your healing, with a healing which does not leave any disease behind).” (Narrated by al-Bukhari (5675) and Muslim (2191)
·        ‘Aishah (may Allah be pleased with her) said: If one of his family fell sick, the Messenger of Allah (peace and blessings of Allah be upon him) would blow over him and recite al-Mu’awwidhat. When he fell sick with his final illness, I started to blow over him and wipe him with his own hand, because it was more blessed than my hand. Narrated by al-Bukhari (5735) and Muslim (2192). 
·        ‘Uthman ibn Abi’l-‘As al-Thaqafi narrated that he complained to the Messenger of Allah (peace and blessings of Allah be upon him) about some pain that he had felt in his body since he became Muslim. The Messenger of Allah (peace and blessings of Allah be upon him) said to him: “Put your hand on the part of your body that hurts and say: ‘Bismillah (in the name of Allah)’ three times, then say seven times: ‘I seek refuge in Allah and His Power from the evil of what I find and I fear.’” (Narrated by Muslim (2202)
·        Abu Sa’id al-Khudri (may Allah be pleased with him) narrated that Jibri (peace be upon him) came to the Prophet (peace and blessings of Allah be upon him) and said: O Muhammad, are you sick? He said: “Yes.” He said: In the name of Allah I perform ruqyah for you, from everything that is harming you, from the evil of every soul or envious eye may Allah heal you, in the name of Allah I perform ruqyah for you. (Narrated by Muslim (2186)
·        Abu’l-Darda (may Allah be pleased with him) said: I heard the Messenger of Allah (peace and blessings of Allah be upon him) say: “Whoever among you suffers some sickness, or his brother suffers some sickness, let him say: ‘Our Lord Allah Who is in heaven, hallowed be Your name, Your will is done in heaven and on earth; as Your mercy is in heaven, bestow it upon the earth. Forgive us our sins. You are the Lord of the good. Send down some of Your mercy and healing upon this pain,’ and he will be healed.” Narrated by Abu Dawud (3892); classed as sahih by al-Hakim in al-Mustadrak (4/243) and as hasan by Ibn Taymiyah in Majmu’ al-Fatawa (3/139). 
·        Ibn ‘Abbas (may Allah be pleased with him) narrated that the Prophet (peace and blessings of Allah be upon him) said: “The one who visits a sick person who is not dying, and says seven times in his presence, ‘I ask Allah the Almighty, the Lord of the Mighty Throne, to heal you,’ Allah will heal him from that sickness.” (Narrated by Abu Dawud (3106); classed as sahih by al-Nawawi in al-Adhkar (p. 180) and by al-Albani in Sahih Abi Dawud) 
Whilst reciting these ruqyahs over yourself, you should wipe your hand over his face, chest and stomach, as the Prophet (peace and blessings of Allah be upon him) used to do, and you should sit near your child’s head so that you will be breathing over him as you recite the ruqyah. There is nothing wrong with blowing lightly onto his face with a little saliva whilst doing that. 
Ibn al-Qayyim said: 
“The ruqyah comes from the heart and mouth of the one who is reciting ruqyah, so if it is accompanied with some of his saliva and breath, that will have a stronger effect.” (Zad al-Ma’ad, 4/164)
Etiquette of du`a
But over and above all that there must be sincerity towards Allah in the du`a , and sincere turning to Him and humility before Him, and one should seek out the times when prayers are answered, for when a person raises his hand to Allah in du`a, He is reluctant that the person should remain empty-handed. 
Do not be hasty in seeking a response, for Allah may delay the answer for a reason that is known to Him, so you should be patient and have certain faith. Remember that the Prophet (peace and blessings of Allah be upon him) said: “Call upon Allah when you are certain of receiving a response, and remember that Allah does not answer a du`a that comes from a heedless heart.” (Narrated by al-Tirmidhi (3479); classed as hasan by al-Shawkani in Tuhfat al-Shakirin (68) and by al-Albani in al-Silsilah al-Sahihah (594) 
Please see also questions no. 3476 , 20176  and 21581 . 
And Allah knows best.