Bringing my wife and two kids to China from Singapore

I am American, my wife is Singaporean and my two kids are Americans. I will have a Z-type soon and have been intending on getting a spousal type for my wife and kids to join me in China once I have a proper entry permit to stay here. But someone told my wife at the Chinese visa agency in Singapore that they would have to leave the country every two months...even if I have a proper z-type and they have a spouse type.

Is this the case?