Un deux trois nous irons au bois is a favourite children's song in France and French-speaking countries such as Belgium, Quebec and Switzerland.
The story of the song
The origin of this children's song is unknown, but it is known to have been sung as early as the 19th century.

Cherries from Provence © French Moments
The song refers to a walk in the woods to pick cherries (les cerises). However, this song is not very accurate. It is very rare to find cherry trees in the woods in France because they grow in orchards not far from the villages.
Un deux trois nous irons au bois
Lyrics, music, free download... let's learn more about the popular song:

The lyrics in French
The original song of Un deux trois nous irons au bois has 1 verse.
Couplet
Un, deux, trois
Nous irons au bois
Quatre, cinq, six
Cueillir des cerises ;
Sept, huit, neuf
Dans mon panier neuf
Dix, onze, douze
Elles seront toutes rouges !
It is possible to add some lines to the official verse of the song:
Treize, quatorze, quinze
Ce s'ra pour le prince ;
Seize, dix-sept, dix-huit
Il préfère les huîtres.
Translation of the lyrics into English
Here is an approximative translation into English:
Verse
One, two, three
We'll go to the woods
Four, five, six
To pick cherries;
Seven, eight, nine
In my new basket
Ten, eleven, twelve
They will all be red!
[Thirteen, fourteen, fifteen
This is for the prince;
Sixteen, seventeen, eighteen
He prefers oysters.]