uk entry requirement for a child with brp accompanied by grandparent

[polymerguy]

Hello everyone, my apologies if my question has been already answered (could not find in the search) or this is the wrong topic.
My 13 years old nephew is arriving in the UK with his grandparent. They both have uk brp cards.
I am wondering if there any addition documents required apart from a permission from the parents for their child to travel with his grandparent. Child's parents are outside the uk at the moment. Mother also have uk brp card.
Many thanks in advance for your help

[zimba]

There will be no issues