回複：B2延期

Your parents had proved the return tendency before they got B1 visa. So, here you do not need to prove again.But if they bring these documents with them, such as certificate of owning house in China and certificate of job, you can attach the copy. Actually, what you want to do here is to tell USCIS that you need their help because your baby is too young, or your parents spent all their times to take care of you and your baby withour visiting America, and right now they have time to visit these places.