In "Birches" by Robert Frost, he speaks of how he wishes that he could swing around from the birch trees like he used to as a kid. It seems as though his identity has changed since he became a child because for some reason now he doesn't go and swing from the birches. Frost says that when he sees the birch trees bent, he wished that it was the work of a playful child.
"Some boy too far from town to learn baseball,
Whose only play was what he found himself,
Summer or winter, and could play alone."
Frost most likely swung from birch trees when he was a child and his identity was being formed. No worries in the world, just having fun. Now he has to worry about things in the real world. He has to pay bills, work, provide for family, not as much free time as when he was a boy.
Frost says that he would love to climb a birch tree all the way up to heaven and then let the tree set him down again. I think that a lot of times, older people probably wished that they could go back to their younger days and be a kid again. At a young age is where most people's identities are formed.
Frost knows that it easily could have been ice or snow that bent the birches down. He wants to feel in himself that it was a boy swinging on his dad's trees. Robert Frost just needs to go play on a playground or swing from a birch and then he wont sound so sad.