i am australian living in shanghai with an F expiring in august...

my son(also australian) who has been living with me here , and on previous 3 month L visa, is going on a holiday to bangkok, before returning to shanghai to leave for Uni in Canada...can he apply for another L tourist in bangkok...he will only be here for 1 month ...I have heard he may need to supply bank accounts and invitation letter , even though he is only visiting with family...is this true??It is his 1st holiday without family(bangkok)and I dont want him to be stranded in bangkok unable to get home to us in shanghai because of this issue...