So, how to say the group which consists of boys only?
The children are upset should be accepted too.
Well, they are trying to make it into a question, so "Are the children upset" would probably be fine while the statement "The children are upset" doesn't really work.
why is the boys wrong flagged
Usually 'yeladim' means a mixed gender group of children.
How would you make כועסים into an English verb? Because "angry" is an adjective. Does it mean "to make angry" or "to become angry" or?
To be angry?
Like you're angry, VS you make someone angry by doing something that angers someone.
Definition of anger
angered; angering play -g(ə-)riŋ
: to make (someone) angry ·He was angered by the decision.
: to become angry ·a man who angers easily
Do the children anger?
Hayladim koasim or choasim?