When designing a Kivy menu with the kv language I run into troubles with the anchorlayout object.
It seems that you need to put every object inside a achorlayout which itself is part of a anchorlayout.

Sounds a bit vague so an example should do:

[sourcecode language=”text”]
<topbox>:
AnchorLayout:
id: topmenu
anchor_x: ‘center’
anchor_y: ‘top’

BoxLayout:
orientation: ‘horizontal’
AnchorLayout:
anchor_x: ‘left’
anchor_y: ‘top’
padding: 8
Button:
id: infobutton
size: (48, 48)
size_hint: None, None
background_normal: ‘info_button.png’
background_down: ‘info_button.png’
on_press: root.on_button_clicked("info")

AnchorLayout:
anchor_x: ‘center’
anchor_y: ‘top’
padding: 8
BoxLayout:
padding: 0
spacing: 4
size: (300, 48)
size_hint: None, None
orientation: ‘horizontal’
AnchorLayout:
anchor_x: ‘center’
anchor_y: ‘top’
Button:
size: (48, 48)
size_hint: None, None
background_normal: ‘star1.png’
on_press: root.on_button_clicked("star1")
AnchorLayout:
anchor_x: ‘center’
anchor_y: ‘top’
Button:
size: (48, 48)
size_hint: None, None
background_normal: ‘star1.png’
on_press: root.on_button_clicked("star2")
AnchorLayout:
anchor_x: ‘right’
anchor_y: ‘top’
padding: 8
Button:
id: quitbutton
size: (48, 48)
size_hint: None, None
background_normal: ‘quit_button.png’
background_down: ‘quit_button_ro.png’
on_press: root.on_quit_button_clicked()

[/sourcecode]