According to the story, this whole debacle started over an argument about Muslim and Christian children crossing the street.
While the media will say this was the cause, it is actually just they symptom. Christians are hated in Egypt and their existence is tenuous. The Christians know this. Likewise, many of the Muslims do not like Christians and look for excuses to harass and attack them.
Thankfully the Egyptian government under Al-Sisi has acted on the case quickly to try and stop further violence, but this is a reflection of the situation on the ground and it does not apppear to be getting better:
A Coptic Orthodox cleric in Egypt’s Minya governorate has said a sectarian attack in a village there on Sunday killed one person and wounded three others.
Bishop Makarious of Minya said in a brief statement Sunday that the families of two priests in the Tahna El-Jabal village were attacked by assailants wielding knives and batons, killing a 27-year-old man and injuring three others, including a woman.
The cleric did not elaborate on the reasons behind the violence, but local media reports suggest the fighting resulted from an argument between Muslim and Christian children over priority to pass through the street.
Emad Nabil, a local lawyer, was quoted in a Christian forum as saying that police had arrested four suspects in relation to the attack. (source)