Theory:

     Every afternoon, when school was over, the children came and played with the Giant. But the little boy whom the Giant loved was never seen again. The Giant was very kind to all the children, yet he longed for his little friend, and often spoke of him. “How I would like to see him!” he used to say.
 
     Years went by, and the Giant grew very old and feeble. He could not play about anymore, so he sat in a huge armchair, and watched the children at their games and admired his garden. “I have many beautiful flowers,” he said; “but the children are the most beautiful flowers of all.”
Explanation:
 
Since the children remained fearless of the giant, they went to the garden every day after their school got over and played there happily. The giant's heart had longed for the little boy's presence in his garden. Yet, the little boy never came to the garden again. Still, the giant treated the other kids with love and care and found happiness amid their presence. He often spoke about the little boy to all the children and explained his desire to see the little boy. But, unfortunately, his wish was never fulfilled.

Many years were gone. The giant became older and weaker. He could no longer play with the kids as he was old. Instead, he observed the kids playing in the garden by sitting on a huge armchair and admired his beautiful garden. Then he said to himself that the children were the most beautiful flowers of all, though he had many flowers in his garden.
 
Meaning of difficult words:
 
S.No
Words
Meaning
1.
FeebleVery weak
2.
Midst In the middle of
3.
AdmireTo look at somebody or something with pleasure or respect
4.
UnfortunatelyUnluckily
Reference:
National Council of Educational Research and Training (2008). The Selfish Giant – Oscar Wilde (pp. 17-24). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.