The US always used to give a step motherly treatment to China only because that country was a negligible partner for US and it used to depend more on US than otherwise.
But the stupendous growth of China in the last ten years has increased the dependence of US on China. Now China is the largest trading partner of US and the inter-dependence is more than ever. So US now wants to have an equal relationship with China and has been recognizing the speedy development of China and also wants to treat China as an equal partner. Good relationship between the two largest nations of the world is good for the whole world.