All French is in Italics, all English is normal. This is the translations, you can do the rest for yourself.

Alouette, gentille Alouette

Alouette, je te plumerai

Lark, nice lark

Lark, I will pluck.

Je te plumerai la tete, je te plumerai la tete

Et la tete, et la tete

I will pluck the head, I will pluck the head

And the head, and the head.

Bec: Beak

Cou: Neck

Ailler: Wings

Dos: Back