We "mainstream" Jews in America are acting more and more like Goyim. I think I’ve done what I could to make my boys as Jewish as I could based on my limited ability. Hebrew names, Jewish day school, trip to Israel for high school kids, etc. My oldest is involved with and plans to marry a woman who even brags about not going to school, who makes terrible life choices, a non practicing Christian. Even in my generation parents would sit Shiva in a situation like this. I’ve told him not to bring her to my home. He obviously knows how I feel. I am without resources to do anything about it.
The only real answer to assimilation is coming to Israel. Here, even someone without a strong Jewish ideology will most likely marry another Jew. If you choose to remain in the Diaspora, a very serious religious Orthodox education is essential - keeping tabs from a young age that the child's identification in terms not only of friends - but also of faith and ideology - is Jewish. Even then, there is no guarantee of success. Assimilation is a mainstream problem in Galut.