Meaning: He was starting to feel sad and frustrated.
Choice of Words: The word discouraged means he was feeling sad and frustrated because he couldn't find the toy.
Alternative Expressions
He was beginning to lose heart.
Meaning: This means that he was starting to feel like giving up or losing hope.
Choice of Words: The verb "was" indicates that the action was happening in the past. "Beginning" means that the action of losing heart had just begun. "To lose heart" means to become discouraged or disheartened.
His spirits were sinking.
Meaning: This means that he was starting to feel down or discouraged.
Choice of Words: The verb "were" indicates that the action was happening in the past. "Sinking" means that something is moving downwards. "Spirits" refers to a person's mood or morale.