Just because a child grows up doesn't mean it stops being a sibling.  It just becomes an adult and begins to be treated as an equal by it's parent.  I'm sure those ex - colonies would be very different places with very different people had the UK never existed.  THerefore by grace of building those countries the UK is a parent country.  Doesn't mean to say those countries are children, they once were, however now they are adult nations themeselves and are now treated equally as a result