I recited this today to old and young alike when a bird was singing in a residential home.
I have looked here to find out more about it for a 6 year old who wishes to learn it.
My remembered version differs very slightly:

Summer has come from a sunny land,
Summer is here again.
Bringing the birdies to sing their songs
In every wood and lane.

Chirruping, chirruping, loud and clear
High in the rocking tree
Dear little birdies i think you sing
Your prettiest songs for me.

But I should very much like to know
How did you learn to sing?
Who was it taught you to sing and fly
And gave you each tiny wing?

"We have a Father", the birdies said,
"Loving and kind and true.
He who has taught us to sing and fly
Will think of the children too".

Thank you , dear birdies, for telling me;
I am so glad to know.
Now when I'm asked, I can always say
"A little bird told me so!"

Tune in key of Fmajor.
C', A, F,C,F,G, A,C',C'.
C',A,F,C,A,G.
D', Bflat, G,D,G,A,Bflat, D',D'.
C'sharp, C',A,F,C,C', F.