Dear Sir/Madam,
With due respect, my name is _________ (name) studying in ___________ class of your reputed school. My roll number/ register number is ________ (roll number).
This is for your kind information that I will be needing leave for ____ (days) due to an emergency situation at my home __________ (mention details). I humbly request you to grant me emergency leave from __/__/____(date).
Kindly, do the needful at the earliest and if you need to contact my parents regarding this matter, you can contact them at _______ (contact number).
Yours sincerely,
___________ (Name),
___________ (Roll number)