Ending in o = neuter, probably. I have to get away from the Italian mindset that ending in o usually means masculine. Then we have the strange German that states: das Mädchen (the girl) is neuter. That is the uniqueness and strangeness of each language.
"ten dziecko" was never correct. I can even see the edits history - which is empty, because there's just no other way of translating "this child" as a standalone phrase, nothing was ever changed here.