Do we need to apply for travel documents or a type of Chinese visa?

My daughter is a US citizen, but was born in Beijing. Her mother is a Chinese citizen (and current US green card holder). Her mother's green card was issued after our child was born. I, the father, am a US citizen. We live in the US now. My wife wants to travel with our daughter to China to see her grandparents for a few months. Also, depending on which service we have to use, must we both be present at the nearest Chinese embassy/consulate or can we hire an agency to do this for us? Thank you.