Harry was so close to the mirror now that his nose was nearly touching that of his reflection.
'Mum?' he whispered. 'Dad?'
They just looked at him, smiling. And slowly, Harry looked into the faces of the other people in the mirror and saw other pairs of green eyes like his, other noses like his, even a little old man who looked as though he had Harry's knobbly knees -- Harry was looking at his family, for the first time in his life.
The Potters smiled and waved at Harry and he stared hungrily back at them, his hands pressed flat against the glass as though he was hoping to fall right through it and reach them. He had a powerful kind of ache inside him, half joy, half terrible sadness.
How long he stood there, he didn't know. The reflections did not fade and he looked and looked until a distant noise bought him back to his senses. He couldn't stay here, he had to find his way back to bed. He tore his eyes away from his mother's face, whispered, 'I'll come back,' and hurried from the room.
From Harry Potter and the Philosopher's Stone
by J K Rowling.