Infidel (literally "unfaithful") is a term used in certain religions for those accused of unbelief in the central tenets of their own religion, for members of another religion, or for the irreligious. Infidel is an ecclesiastical term in Christianity around which the Church developed a body of theology that deals with the concept of infidelity, which makes a clear differentiation between those who were baptized and followed the teachings of the Church versus those who are outside the faith. The term infidel was used by Christians to describe those perceived as the enemies of Christianity.
There is no disbelieving child even if his parents were disbelievers. Children are born on the distinct (Fitra) which has dasics of faith. No one will be punished by a Allah, The Glorious, before knowing and insisting on denying the truth after knowing the truth. Children who die in their childhood will be given on the Day of resurrection full option to know the truth then decide. If they accept the truth, they will be in the Paradise.
The real father of Ebrahim was a believer as we read in Quran that Ebrahim prayed for his parents ( O My Lord, Forgive me and my parents on the Day of Judgement) (Sura Ebrahim, Verse 41). It is not allowed to pray for forgiveness of polytheist. (Sura Al-Tawbah, verse 114) which is clear that Ebrahim did not pray for his disbeliever uncle but did pray for his believer real father.
Azar who was mentioned in Quran (Sura Al-An'am, Verse 74) was not the real father of Ebrahim, but was his uncle. His real father's name is Taarih تارح. Arabic language allows to call the uncle as father أبو but the real father is called والد parent.
'In Quran, Allah (SWT) mentioned Esmael as one of the fathers of Yaqoub Jacob though he was his uncle (Sura Al-Baqara, verse 133).
Thank you for your question. This depends heavily on the maturity of the child, but while a child may be convinced of religion or not, they are not taken account for their actions or their beliefs until they reach an age of maturity. On the other hand, if they commit good actions with belief they will be rewarded.
May you always be successful
Thank you for your question. The problem with many questions such as this is that they are not usually framed realistically. Is it really realistic for someone who does not believe in the religion of Islam to perform all of his or her actions according to its dictates? If that is not possible or unrealistic then this question is completely hypothetical. God will ultimately judge every person, but the value of being in the fold of Islam is such that in this hypothetical situation the Muslim will have a better end as the Prophet (saw) will intercede for the major sinners in his community, if they have the capacity to be interceded for.
May you always be successful
May you always be successful.