I'm going to look for English songs especially suitable for standard 4,5 and 6.

I don't have any ideas for the suitable songs!! So far as I know, the song like, "Heal the world" is good for suitable to sing.

Any other songs?
which standard do you refer to exactly?

standard 4 or 5 or 6. Which song is suitable?
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By "standard", did you mean "school grades"?