Contentment from a 9-yr old

We attended a birthday party of a friend's daughter.
The host invited all the children to gather. First game was "Guess the Riddle" wherein the host gives the riddle and the first child to give the correct answer receives a prize. The first riddle was given, Honey raised her hand and gave the answer. Her answer is correct. She collected her reward and return to our seat. I told her to go back to the game area as the game is not yet done. She just stared at me. Then comes the second riddle. I saw her smile, I know she knows the answer. I told her to raise her hand and answer again. She didn't listen. Then the third riddle, she still knows it.
"Ate, answer the riddle so you can get another reward", I told her.
"But I already have a reward Ma!, ang uban nasad!", she snapped.
("But I already have a reward Ma!, give others the chance!")

Now, its my turn to stare her. 
Silent. 
Thinking.
Was I teaching my kid to become selfish?
Was my action reflects discontentment?

I understand her simple happiness with the reward she received and for her its already a treat, already enough.

Then I remembered Moses' instruction on getting enough manna needed for the day yet the people didn't listen, thus the manna was spoiled. 

If only adults think the way like the children...
If only adults learn to be contented in small things...
if only adults listens...

...then life would have been simpler, more comfortable and fulfilled.