Meaning: The young people were making a sound of happiness at the same time as they were taking part in an activity for enjoyment in a loose material made of small rocks and minerals.
Choice of Words: Children are young people. Laughed means they were making a sound of happiness. Happily means they were feeling happy. As means at the same time. They means the children. Played means they were taking part in an activity for enjoyment. Sand is a loose material made of small rocks and minerals.