can't select self-children items
`item.children` is exposed as a select query, which is iterable. Do this:

```python
a = A.get(...)
for child in a.children:
    print(child)
```

Also post questions like this on stack overflow. Self-referential fk docs are here for your reference: http://docs.peewee-orm.com/en/latest/peewee/models.html#self-referential-foreign-keys
``` Python
class A(BaseModel):
      parent = ForieginField('self', null=True, backref='children')


for item in A.select():
    print(item.children)
```