It's funny being forced to write "you all" or "y'all" randomly because it's not in my dialect, so my brain immediately wants to add other things I think of as Southern US dialect (but may not actually be).
I think it is the ending "ni" that refers to second person plural which is not clear in the english translation unless it is put like that.. as awkward as it is. The verb ending "ni" refers to the subjects "nyinyi".
"wakicheza" would be better here. As it is the sentence reads like "Look, the children are playing". The "ki" is used like the "ing" in a sentence like this or "I saw him sleeping" - "Niliona yeye akilala"