First of all, I-485 is Adjustment of Status, which is the process to get the
green card in the U.S. Your parents are not in the U.S., so they will not
do Adjustment of Status. They will do Consular Processing, which is a
different process. I-485 will not be involved.
There are two stages. You file I-130, and once it is approved, then they go
through Consular Processing with the consulate in China. When they get to
the Consular Processing stage, they will definitely not be able to enter on
a B2. A pending petition (I-130) does not technically prevent them from
visiting on a B2 visa, especially for categories with really long waits like
siblings, but for parents, a category with no wait, they are very unlikely
to be able to enter on it, because it is so easy for them to abuse it and
immigrate once in the U.S.