Theory:

     Velu put his head down on his knees, feeling miserable and exhausted. He had run away from his village two days ago. For two days he had eaten nothing but some peanuts and a piece of jaggery. In his bundle he carried a shirt, a towel and a comb.
 
     He had walked for most of the first day to Kanur and then got on the train to Chennai. Velu had no money for a ticket but luckily the ticket collector didn’t come to the unreserved compartment. He had tried to sleep on the floor near the door. A group of men next to him had played cards and shouted all night.
Explanation:
 
Velu felt irritated and miserable due to the large crowd and the loud noises from the television. After a while, Velu bent down his head over the knees, as he felt very dull and tired.
 
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Velu put his head down on his knees

Velu felt very tired because he had not eaten anything except a few peanuts and some jaggery. (Jaggery is a variety of sweet used in many South Indian dishes like payasam to give an excellent taste).
 
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Jaggery
 
Velu carried a small bag with him before leaving his village. Velu took a shirt, comb, and a towel in the bag.

After getting out of his home, Velu had walked a long way and reached a place called "Kanur". From Kanur, he decided to reach a railway station. After reaching the railway station, Velu saw a train, and it was the Kanyakumari express. The train would reach Chennai Central by the next day. To travel on a train, one must carry a train ticket while boarding. Unfortunately, Velu has no money to buy a ticket. It is later revealed that his father was quite abusive and was in the habit of taking away all his money. So it is possible that the father was the reason why he couldn't afford the ticket. Without money and a ticket, Velu got on the train. Luckily, the ticket collector (also known as Travelling Ticket examiner) did not come to the unreserved compartment for checking tickets. Once the train started from Kanur, Velu took a deep breath, and he thought of sleeping for a while. He tried to take a nap on the floor near the door. But he could not sleep because a group of men were sitting next to him and playing cards. The men were shouting the whole night. It made Velu stay awake throughout the entire night.
 
Meanings from the difficult words:
 
S.No
Words
Meanings
1
MiserableA state of feeling unhappy or uncomfortable
2
ExhaustedA state of feeling extremely tired
3
UnreservedNot booked in advance
4
PeanutsThe oval seed of a tropical South American plant, often roasted and salted and eaten as a snack or used to make oil
Reference:
National Council of Educational Research and Training (2008). It so happened. Children at work- Gita Wolf, Anushka Ravishankar and Orijit Sen (pp. 7-16). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.