He was not a child.
It was true that sometimes he smiled like a child and dreamed like a child and did many childish things, but in the end of it all he was old. Older than most. Older than almost anyone.
He saw death and sadness and anger and it made him so, so old.
There were others once. Many others. And they were fabulous and young and adventurous and willing to trust a daft old man and his blue box.
One by one, he had let each of them down.
There had been Rose, brilliant, stunning Rose with a smile like the sun rising and a heart he had called home. Now she was locked away, living a life with a Doctor that was not him. Living every day, walking the shore of a world that was Earth but not Earth, going home at night to a father and a mother and brother – things she never could have had with him.
Then had come Martha, so clever, a doctor in her own right. Who had seen her future with him and been wise enough to leave while she could. Who found Mickey, of all people, and was happy with him. Martha Jones and Mickey Smith and the rest of their lives stretched out before them – long lives, another rare occurrence in his travels.
Following so quickly after had been Donna the quick, the funny, the loyal. Who would never leave him behind or let him down. Brave to a fault. A fault that would cost her so terribly. She lived, but was dead. Thinking herself forever a useless temp who was only good for a laugh. She had found some happiness, of course, some of his doing, but still – gone and never remembering how the universe owed her its existence.
Then Amy, fiery, sharp-tongued Amy and the Last Centurion trailing on her heels. The girl who had waited for him all her life only to follow him to her death. She strolled along streets, ate meals every day, lived a life in a time sealed off from the universe. The Ponds and their son, who lived every day for forty years, trapped in New York with the knowledge that he had abandoned them – with the knowledge that there were people back home who wept for them.
There should have been another.
Clara or Oswin or Oswald, whichever name she happened to be using. First a Dalek, then a governess, never in the same place twice and slipping from his reach both times. The Girl Twice Dead that skipped through time – or rather, time did not want him to find her.
All this sadness, this sorrow, this emptiness found him doing another childish thing.
He sat on the swing.
He had been so close this time. Wandering for ages, looking through planets, waiting for the universe to make good on its debt. He had saved the Earth, so she deserved to live.
So when he landed shortly before the turn of the century, he had been so, so hopeful. This was it. This time for sure. No more guessing, no more lonely escapades, no more long days on a cloud.
He forlornly watched the children running and shrieking as they catapulted from one end of the playground to the other. So young. So very, very young and free of guilt and sadness.
He speaks with her. She is lively and full of energy and so very alive. Not scared or dying, but a breathing living child who is too young to travel with him.
He wonders if she will ever be old enough to travel with him. If he weren't so terribly selfish, he would leave her to her life. She would continue to live and maybe meet a nice boy and die of old age surrounded by those she loved. What a refreshing ending that would be.
But he is not good enough. For all his age, his tiredness, his grief... he is still a selfish child.
And so he leaves his swing as she runs off to live another day.
He will find her.
She will live.
The ending will be different this time.
And the Doctor is just enough of a child to hope this is true.