Why are Jonas and his father worried about Gabriel's fretfulness at night, and how did Jonas try to solve the problem in The Giver?

Both his father and Jonas are concerned that Gabriel is fretful at night because sleeping through the night is required of the new children. If the newchild continues to not sleep well at night, he will be released.

Dispassionately, Jonas's father tells the family in their "evening telling of feelings" that it is rare that the status of a newchild such as Gabriel would be so uncertain. But, he adds,

"Right now we're all preparing for a Release we'll probably have to make soon."

Alarmed by these words of his father, Jonas suggests that the baby's crib be moved into his room for the night. He tells his parents that since he knows how to feed and comfort Gabriel, the parents could get a good night's rest by letting him care for Gabriel. Worried that Jonas is such a sound sleeper, his father is reluctant to do this. But, when Lily points out that Gabriel cries so loudly that even Jonas will awaken, Father agrees to "...try it, just for tonight."

When Gabriel awakens in the middle of the night, Jonas hears him and goes to his crib. He is able to get the baby back to sleep by rubbing his back. However, Gabriel continues to stir and awaken throughout the night; so, Jonas continues his rubbing of the infant's back to get Gabriel to fall asleep. One time, as he stands quietly beside the crib, Jonas's memory is stirred, and he recalls a memory shared with him by the Giver:

...a bright, breezy day on a clear turquoise lake, and above him the white sail of the boat billowing as he moved along in the brisk wind.

Then, as Jonas recalls this memory, he feels it slide through the hand he has on the back of the baby. Startled, he quickly removes his hand, retrieving what he has left of the memory. But now, the baby sleeps well. When he stirs near dawn, Jonas impulsively decides to give Gabriel the remainder of the memory by placing his hand once more on the baby's back.

By giving Gabriel a memory, Jonas has taken a personal action for which he has no authority:

He was not yet qualified to be a Giver himself, nor had Gabriel been selected to be Receiver.

Frightened by his new power, Jonas decides to keep his act of sharing his memory with Gabriel a secret. There is also in Jonas a burgeoning feeling of anxiety about the conditions that exist in his society. For, he wonders about Elsewhere and how easily his parents speak of this place where Gabriel may be sent. Also, Jonas is concerned about the fact that his father mentions so dispassionately that if Gabriel is released, there is another set of twins due to be born very soon. When his father will be the one to select which one will live in the community and which one will be released, Jonas feels uneasiness, as well as wondering where these human beings all go.