CollectionProperty of Object.children

Coding Python Support
2

template_list is designed for CollectionProperties, which is like a 1-dimensional array of hashmaps (or in python lingo: a list of dicts).
It’s not really suitable for nesting like you desire.

I don’t think template_list is needed for what you want. You could just do something like:

import bpy


class HelloWorldPanel(bpy.types.Panel):
    """Creates a Panel in the Object properties window"""
    bl_label = "Children"
    bl_idname = "OBJECT_PT_hello"
    bl_space_type = 'PROPERTIES'
    bl_region_type = 'WINDOW'
    bl_context = "object"

    def draw(self, context):
        layout = self.layout
        start_ob = context.object

        def child(ob, level=0):
            row = layout.row()
                
            for i in range(level*3):
                row.separator() # FIXME
            row.label(icon="FILE_PARENT" if level else "OBJECT_DATA")
            row.prop(ob, "name", text="")
            for child_ob in ob.children:
                child(child_ob, level+1)
                
        child(start_ob)


def register():
    bpy.utils.register_class(HelloWorldPanel)


def unregister():
    bpy.utils.unregister_class(HelloWorldPanel)


if __name__ == "__main__":
    register()