The Girlie has the ability to count things, but not yet to realistically assess size / amount.
So I will, say, give The Kid a piece of toast cut into four pieces. The Girlie will demand that she, too, wants toast. I will know that if I give her the exact same amount, then she won't eat it all - she will only eat about half. But! If I give her only two pieces - half of what The Kid had - then she will protest at having been given less than The Kid.
So what do I do? I give her half a toast - half the amount The Kid had - but I cut it into four pieces. The Girlie will count the pieces (four!) and be happy that she's been given the same number of toast pieces as The Kid. I will be happy that I haven't needed to waste toast.