If they had been interested enough they could have been registered at their home address from the date they were eligible - for all elections. In times past (before internet registration) students did this and obtained a postal vote if required.
Here are some links regarding schoolchildren, the referendum and "voting":
http://www.manchestereveningnews.co.uk/news/greater-manchester-news/eight-year-old-begs-mum-11506939
https://www.tes.com/news/school-new...-shows-clear-majority-teachers-want-remain-eu
https://www.tes.com/news/school-news/breaking-news/schoolchildren-vote-remain-eu
Note the tender ages of these children. Note also the middle link about the majority (a big majority) of teachers wanting to remain. There have been plenty of complaints on this forum and others, about teachers pushing their vegetarian ideas. I feel the same about what dthey did leading up to the referendum.
Not that it matters, because we are leaving. I would not be surprised if Juncker insists we are thrown out before Christmas.
Don't kid yourself , they NEED our money.