Children aged 17 or younger travelling to Portugal alone or with someone who is not their parent or legal guardian will need a letter of authorisation in order to travel there. What does the letter to enter Portugal need to include? The letter must be issued alongside a copy of the child’s parent’s or guardian’s passport. If a child is a resident of Portugal and aged 17 or under, they "must carry a properly certified letter of authorisation if travelling without their parent or legal guardian." Did you know these rules were in place for travelling to Portugal?