Language is just one clear sign of the cultural gap for people living abroad, religion could be another.
In most Vietnamese families, the spinal religion can be considered as the cult for ancestors, and the respect for elder people, included their parents. This religion/culture creates the mental and spiritual skeleton of the family and help it strive. It helps to bring the story from one generation to another, make the children proud of their origin and guide their decisions and acts.
Although this culture/religion is very important, it can be considered as a culture trait rather than an organised religion. Unlike Christianity or any other religions, it isn't well defined and does not involve establishment and timely gatherings for worshiping and learning. The cult for ancestors and respect of elderly are not a religion to practice with enshrined books or Bible. It can be lost, diluted if not cared for enough. Living alone in a new country, far from the bigger families, having no grandparents, this religion/culture can be forgotten and not practiced in everyday family life, creating a cultural gap or fracture. Compared with native children of native families with established religions like Christianity or Muslim or even those without religion but having a tight net of family and relatives, these Vietnamese immigrant families could suffer some spiritual disadvantages and drawbacks.
This is particularly true nowadays when children are under continuous attractive invasion from social media. Without a solid background that hold them back, they are like mayflies who precipitate to the attraction of social media with all nonsense praising for self harming and self indulgent hobbies of posting and texting. It is a lot of time lost. Following by other dangerous things like bad influences, self centering, being obsessed by physical appearance, self harming.
I have stated from the beginning that the context of this worry is for family abroad. However cultural/spiritual fracture and its consequence could also involve family living inside of Vietnam nowadays.
To some extent family is like society and like politics, we need always the conservatives that hold back against the negative effect of the progressive trends. We do never know.