My two year old was crying in the backseat today, upset that his juice cup was empty and I couldn't refill it.
The 6 year old consoled him. "Apple juice is not milk, Little D. When you were littler, Mom could make milk for you when you cried but she can't make apple juice just because you're crying - it's not that easy anymore. So please stop crying."
I love how simply he explained such a complicated thing -- "It's not that easy anymore."