L or S2 visa for visiting my son

I am planning to visit my son and daughter in law in China and am not sure what the advantage is of an S2 over a Tourist L. They both have residence permits for work in China. The S2 requires proof of the family relationship ie his birth certificate which is with him in China - so that would have to be sent home for the application to be made! So I'm thinking the L type would be much more straightforward. I would like to get a multiple entry one as they are expecting their first baby but for relatively short visits of no more than two weeks - and I don't know if that has any bearing on the question of S2 or L. Any help would be appreciated. Thank you.