The child was left crying in the street.

Çocuk sokağa ağlar halde bırakıldı/bırakılmıştı.

or

Çocuk sokakta ağlar halde bırakıldı/bırakılmıştı.

I think sentence means the first translation. But I am not sure.

Çocuğu sokakta ağlar halde bıraktılar.

ağlar halde...yes! It was over my tongue but I couldn´t get it out. Thank you, gokuyum and ikiciihan, like always.

Who is crying? The child, or those who left him on the street?

Of course the child.

That was the problem. No matter how I was trying to express it it was always the wrong people who were crying.

A comma missing somewhere?   

Where?

comma not necessary at all but if you still want to use it, use after "çocuğu".

in some extreme thinking, "çocuğu ağlar halde" may be an adjective of a sad woman. the woman was left in the street with her crying child! meaning is not this but 1 out of a 1000 may think this, to prevent misunderstanding we can use comma after "cocuğu".

if we use "çocuğu sokakta ağlar halde", comma not necessary.

finally we express this with or without comma like below:

Çocuğu sokakta ağlar halde bıraktılar.

or with comma

Çocuğu, ağlar halde sokakta bıraktılar.