Worried - don't have 3 months remaining on my son's passport...

Hi, my 5 year old son (Japanese and British national and passports holder) and I (British) will arrive in Shanghai Pudong on the 14th Aug late afternoon, and travelling out again on the morning of the 15th. However both of my son's passports expire in September. Will he be able to enter China on a 24 hour transit visa or will we need to stay airside overnight?