Translation:A child has been born
This is the passive voice. I think that the verb kuzaliwa ("to be born") refers to the actual act of being birthed, as in emerging from the birthing canal. So 'mtoto anazaliwa' = a child is being born (at this moment, the child is being birthed) 'Mtoto alizaliwa' = a child was birthed 'Mtoto amezaliwa' = a child has been birthed (and is still alive). In English, we might say 'a child is born.'
This way of speaking was once correct, though it has certainly fallen out of use by now. "To be" was used with intransitive passive words. We can see an example of this in the song "Joy to the World" in the first line: "Joy to the world, the Lord IS come." This form of speech is also common in Italian, and I think French, too. "Lui è venuto" = "He is (has) come"