kivy_problem.py

from kivy.app import App
from kivy.uix.scatter import Scatter
from kivy.lang import Builder


KV = '''
FloatLayout:
    MyScatter:
        size:1000, 1000
        do_rotation: False
        size_hint: None, None
        auto_bring_to_front: False
        Widget:
            canvas:
                Color:
                Line:
                    rectangle: [0, 0, 300, 300]
                Rectangle:
                    pos: 20, 20
                    size: 10, 10
    Label:
        id: my_label
        text: '<-- Small rectangle top is here'
        size_hint: None, None
        size: self.texture_size
        x: 30
        center_y: self.height and 30
        font_size: '20sp'
'''


class MyScatter(Scatter):

    def on_transform_with_touch(self, touch):
        #get the label
        label = app.root.ids.my_label
        #hardcoded pos,
        #given the size and font of the label,
        #this will point exactly to the small rectangles top
        #...until the scatter is scaled
        x, y = 30, 30
        #move the label
        label.x, label.center_y = self.to_parent(x, y)


class MyApp(App):
    def build(self):
        self.root = Builder.load_string(KV)
        return self.root

if __name__ == "__main__":
    app=MyApp()
    app.run()