Differentiating parent nodes from children in node network

I'm building a JS application that involves manipulating node networks. I'm finding JSPlumb to be incredibly difficult to integrate, so I'd like to differentiate parent-child relationships in the graph in a way that doesn't involve directed lines / arrows.

These are what my nodes look like right now, where j2a... is the child of root: What would be an effective way of displaying a parent-child relationship here, possibly through the use of color? The easy solution I'm considering is filling those [ ] brackets with the name of the node's parent, but I don't think that will be enough of a visual differentiation.