Youngs Boys Playing With Genitals
Question

                My son is four and a half years old. I have started to notice that he sometimes puts his hand into his underwear to move the underpants away from his body. When I told him off for putting his hand in this place he said that it hurts in this area, meaning that he had an erection. So I took off his underwear and left him in regular pants. Now he prefers to stay at home with no underpants. Was this a mistake? Can I let him get used to that?
Praise be to Allah.We appreciate your keenness 
    to take care in raising your children, which is something that many people 
    are careless about, even though there are commands in the Qur’aan and Sunnah 
    which enjoin protecting oneself and one’s family from the Fire, being 
    sincere towards them, taking care of them and paying attention to their 
    spiritual affairs such as prayer, and making them sleep in separate beds. 
Allaah says (interpretation 
    of the meaning): 
“O you who believe! Ward 
    off yourselves and your families against a Fire (Hell) whose fuel is men and 
    stones, over which are (appointed) angels stern (and) severe, who disobey 
    not, (from executing) the Commands they receive from Allaah, but do that 
    which they are commanded.”
[al-Tahreem 66:6]
It was narrated that 
    ‘Abd-Allaah ibn ‘Umar said: I heard the Messenger of Allaah  (peace and 
    blessings of Allaah be upon him) say:

    “Each of you is a shepherd and each of you is responsible for 
    his flock. The ruler of the people is a shepherd and is responsible for his 
    flock. A man is the shepherd of his household and is responsible for his 
    flock. A woman is the shepherd of her husband’s house and children and is 
    responsible for her flock. The slave is the shepherd of his master’s wealth 
    and is responsible for it. Each of you is a shepherd and each of you is 
    responsible for his flock.” 
Narrated by al-Bukhaari 
    (853) and Muslim (1829). 
It was narrated that Ma’qil 
    ibn Yasaar said: I heard the Prophet  (peace and blessings of Allaah be 
    upon him) say: “There is no one whom Allaah puts in charge of a group of 
    people then he fails to take care of them, but he will not smell the 
    fragrance of Paradise.” 
Narrated by al-Bukhaari 
    (6731). 
Your noticing your son’s 
    movements is indicative of your concern to make him get used to good 
    attributes and avoid bad attributes. This is a good thing, but at the age 
    which you say your son is – four years old – sexual urges have not appeared 
    in the majority of children. Some research has shown that it is possible for 
    sexual urges to appear in some children before puberty, which is manifested 
    in playing with the genitals for the purpose of sexual enjoyment. Some 
    educators believe that this habit begins at the age of nine in ten percent 
    of children, and others think that it may start between the ages of two and 
    six. [See: ‘Adnaan Saalih Bahaarith: Mas’ooliyat al-Abb al-Muslim fi 
    Tarbiyat al-Walad fi Marhalat al-Tufoolah, p. 468] 
A father often sees a child 
    of this age putting his hand on his genitals without noticing, and if he is 
    told, he will pay attention and remove his hand.  
The reason for that in some 
    cases may be because there is an itch or an infection in that place, because 
    the mother has been overzealous in cleaning him, or the cause of the 
    infection may be negligence in cleaning the child after urinating or 
    defecating. 
Another reason why a child 
    may be interested in his private part is that he has been given the 
    opportunity to play with it by being left naked for lengthy periods, so he 
    starts to look at it and play with it. What should be done is to make the 
    child get used to being covered from a young age, and put him off the idea 
    of remaining naked. 
If the child is seen 
    placing his hand on his private part, he should be distracted with something 
    else, such as giving him a toy or a cookie, or by hugging him and kissing 
    him. 
The aim is to distract him 
    from this habit by simple means without making a fuss. There is no need to 
    scold him harshly, because that will only make him more curious about that 
    area and find out why he isn’t allowed to play with it. 
There is nothing wrong with 
    asking the child if he has an itch or a pain in that area which is making 
    him play with himself. 
Op.cit., p. 472 
With regard to your son’s 
    issue in particular, we think that you should make sure that there is no 
    problem in his clothes or body that is making him do that. Try to dress him 
    in loose underwear and do not leave him wearing his outer pants only. 
Whatever the case: 
We advise fathers and 
    mothers that it is essential to make their children get used to being 
    covered and modest, and not let them wear short clothes, whether they are 
    male or female. They should get used to wearing concealing clothes when they 
    are still small, so that they will grow up chaste and decent. 
Shaykh Muhammad ibn Saalih 
    al-‘Uthaymeen (may Allaah have mercy on him) said: 
It is well known that if a 
    person is influenced by something when he is small, he will remain 
    influenced by it when he grows up. Hence the Prophet  (peace and 
    blessings of Allaah be upon him) enjoined us to tell our children to pray 
    when they are seven years old and to smack them (lightly)if they do not pray  when they are ten, so that they will get used to it, and the child will follow what he has gotten used to. 
Al-Liqa’ al-Shahri, 
    66/ question no. 9 
See also the answer to 
    question no. 43485 and 
    9909. 
And Allaah knows best.