Answered by ZUPAN | Nov. 18, 2019 23:04
OK, it's quite clear now :)
Actually, since the parents already have visas they cannot apply for any other because it is not possible. Anyway, since the children don't have visas, probably the best solution would be to obtain the visas for children upon arrival in Hong Kong. They can obtain them or through Hong Kong CVASC or through some of reliable agencies. The agency can obtain rush visa for a bit higher price, but really fast. Like this, the whole family will be able to travel to Xiamen with complete peace of mind. Also, it will be also possible to accomplish the business appointment in Xiamen, but it is not necessary that a father tells that to the immigration authorities. They will just tell that they have arrived in Xiamen for tourist purposes and that's it.
Just to clear the picture... Polish citizens don't need a visa for Hong Kong, so they are fine there. So, they will use their tourist visas, the parents those already obtained and children those obtained in Hong Kong. It is required roughly 3 working days if they apply for a rush visa service, but they should contact an agency in advance and to make (to resolve) all the possible details they can online. This will allow them not to spend too much time in Hong Kong.
Now, if the next city after Xiamen where the mentioned family is traveling is outside China, the children don't need any kind of visa, but if their next destination is within China, they need a visa. In reality, by far the best situation is as I have already mentioned. The parents will just proceed to Xiamen by using their tourist visas and they will obtain the visas for their children in Hong Kong by submitting most of the details to the agency online.