The children were playing happily.

Meaning: This sentence is describing the children as playing and feeling happy. It's like saying, The children are taking part in an activity for enjoyment and feeling very happy.

Choice of Words: Children are young people. Playing means taking part in an activity for enjoyment. Happily means in a state of great joy and contentment. This sentence describes the children as taking part in an activity for enjoyment and feeling great joy and contentment.

Alternative Expressions

Related Expressions