Meaning: The children are enjoying themselves by moving back and forth on the swing.
Choice of Words: Happy describes the children, children are the people, play describes the action they take, on describes the location, and swing is the object.
Alternative Expressions
Joyful youngsters swing merrily.
Meaning: This also means that some young people are having a good time playing on a swing.
Choice of Words:Joyful is another way to say happy or delighted. Youngsters is a more formal way to refer to children. Swing is the same as before. Merrily means in a happy and cheerful manner. This sentence uses more sophisticated vocabulary to convey the same meaning as the first one.
The children are having a blast on the swing set.
Meaning: This also means that some young people are having a good time playing on a swing.
Choice of Words:Blast is an informal way to say a really good time. Swing set is another way to refer to a swing. This sentence uses more casual language to convey the same meaning as the first two sentences.