@viques@Growlybear83
All of what I am about to say is about the Republic of Ireland, but it is apparent from the OP that the one-week Halloween school break is standard in N.I. too.
Halloween is a key date in the calendar in Ireland. The Celtic festival of Samhain which has been celebrated/marked since time immemorial on this island has been Halloween for many hundreds of years.
Schools in Ireland break for one week at Halloween. In Ireland, the mid-term break doesn’t occasionally conincide with Halloween, rather the mid-term break is absolutely always at Halloween. It is the Halloween break.
Halloween may be new to parts of the UK [largely indirectly imported from the US, rather than directly from Ireland (and Scotland)]. However, it long pre-dates the school system itself in Ireland. It is in no way new-fangled here, but rather an indigenous special tradition-laden day and period that children in particular are involved in: special games, special fruit bread (barmbrack), dressing up, trick-or-treating, play-casting spells and telling the future with apple peels and all the rest. Halloween was as contemporary to our grandparents’ grandparents as it is to us, and was always a feast day.
Aside from the one-week Halloween Break at schools, the last Monday of October is a Bank Holiday in Ireland, i.e. the Halloween bank holiday. This year the official bank holiday for workers fell on 30 October.
Wikipedia: “Celebrated in Ireland and Scotland for centuries, Irish and Scottish immigrants took many Halloween customs to North America in the 19th century, and then through American influence various Halloween customs spread to other countries by the late 20th and early 21st century.”
https://en.m.wikipedia.org/wiki/Halloween