You should watch Gangs of New York. It highlights how the original white anglo saxon Protestant population of americans had the same fears as you mentioned with catholic italian and irishmen coming in and changing the culture of the country.

It turns out, everyones kids assimilate into american culture just fine. Today you can’t tell whether a kid came from an anglo or irish or italian background. In some parts of the US that is already true for latinos, who are now the dominant population in many american cities, and whose youth population engaged with the same things as any other american youth population today.