There appear to be pencil marks sketched under the faces, which suggests that this is painted rather than a print. The edges of the black and dark blue on the lighter colors, and the lighter blue marks on the dark blue shirt, look to me like they were painted with a brush.
I agree that this looks quite sophisticated to be a child's work, at least probably not by a pre-teen. Student work, possibly.
I'm not sure what you mean by "block art" but I think this looks like a painting, not a print. The edge of the tan background over the green could possibly be a registration mark in a serigraph (screen print) or a block print, but based on the other indications that suggest a painting, that seems more likely.
At least in the 80s, when I took some fine arts classes including printmaking in university, many professional artists had and used chops to ID their work. So the presence of a chop mark (the printed asian characters) does not necessarily mean that the artist was Asian.
