Hello, transit in china with less than 3 months passport valid

I will be transiting in China with my kids in August and my son has his passport expired in close to 3 months from the date of flight into China.
A couple of questions - will he be allowed to enter China (I mean board the flight) and will he be legible for TVOW 72 hours (Russian passport) in Beijing or I better buy him a ticket with the shortest transit possible without leaving the transfer area in PEK. Thanks!