I applied for a UK work visa recently and when filling the form I answered “no” with respect to have you ever been refused visa to the UK. However upon discussion with my parents I was informed I was refused a visiting visa as a minor (14 years) 12 years ago. Do I need to update my application as I am yet to do my biometrics.
Yes, you definitely should update your application.
Contact UKVI using the link Traveller gave you, with an explanation of what happened. You may possibly be refused a visa, but giving false information on a visa application - intentional or not - can be considered deception and might get you a ban. UK visa authorities can pull up your records and so will know about your refusal. Your explanation seems reasonable to me, and even at age 14 the refusal is not going to weigh very heavily against you.