Children who have reached the age of ten must be separated in their beds
Question

                Is it permissible for me to sleep beside my friend with only one blanket when we do not have anything else to protect us from the cold, or if there are two blankets but they do not protect against the cold unless they are used together?.
Praise be to Allah.
    It is not permissible for two who have reached the age of 
    puberty to sleep together under one blanket. The Prophet  (peace and 
    blessings of Allaah be upon him) said: “Teach your children to pray when 
    they are seven years old and smack them if they do not do so when they are 
    ten years old, and separate them in their beds.” Narrated by Ahmad, 6689; 
    Abu Dawood, 495; classed as saheeh by al-Albaani. 

    If this is the ruling concerning those who are ten years old, 
    then how about those who are older than that, who should not be in one bed 
    but rather should be in two separate beds with two separate blankets? If 
    there are only two covers and one of them is not sufficient to ward off the 
    cold, then each person should take one cover and fold it in half so that it 
    will be thicker and will ward off the cold, or he should buy another 
    blanket. 
Al-Haafiz ibn Hajar said concerning a number of people sleeping in one bed: It was proven via another isnaad that this is subject to the condition that they do not sleep under one blanket.  Fath al-Baari, 7/204.