We had baby last Feb. So, Me any my wife decided to call our parents before the birth of our baby. I asked my in-laws to apply for the visa first. They went for the visa, and consulate asked couple of questions like why they are going and how long they will stay etc, etc, and they both got the visa. 

After our baby was born, In April, I asked my parents to apply for the visa, and they also got asked same questions. They also got the visa. Both time our parents mentioned that, they are going to visit our new son. Since he was the eldest grand child, thats why they wanted to visit us. Here are the document which they used

(from us)
Form I-134 (My wife was main sponsor when her parents applied and I was the main one when my parents applied)
Sponsorship letter stating that My wife will sponsor her parents. (when My parent applied, I changed such that I am going to sponsor my parent)
Bank Letter showing that we have enough fund to support our parents (We had some savings saved for our baby)
Letter to Consulate to grant visa from us

(Extra Document Used from our parents)
Our Wedding photo
Nepal ko ghar ko Lal Purja
(In case of my parents, they put the picture of our baby too as baby was already born in February and They applied for visa in April)


I dont think you need to send the Tax Documents or Employee Letter. When our parents fill the form back in Nepal for visa date, they have to give our Employer information with the address and the phone number.  You need to fill your salary information in FormI-134 so I didnot send my Paycheck too. Just to let you know, when our parents applied for Visa, we were not Green card holder. We were here in H1B, but in the process of getting green card though.

Using above documents, one of my friend's parent too applied for the visa, and they got the visa too.