A funny thing happened on the way from the '60s. Children of immigrants, instead of exhibiting better health than their parents, began to show signs of deterioration: The more acculturated teens were, the more risky behavior they displayed.
Marielena Lara and colleagues, in a 2005 review of the literature, notes the overall health findings are complex. But "the strongest evidence points toward a negative effect of acculturation on health behaviors overall -- substance abuse, diet and birth outcomes (low birth weight and prematurity) -- among Latinos living in the United States." This was true even though acculturated Latinos were more likely to use preventive health services of various kinds.
-Maggie Gallagher, "America's Other Assimilation Problem"
Jim Kalb provides a similar discussion:
...increased English use by immigrants leads to teen sexual activity. The numbers are impressive. Among Hispanic teenagers in Arizona, 13.6% of Spanish speakers, 24.4% of bilinguals, and 30.7% of English speakers have engaged in sexual intercourse. (The rate for whites is the same as the rate for bilingual Hispanics.)
Neocon immigration enthusiasts point out that assimilation still works: the children of Chinese immigrants like the same pop culture American teenagers like. That's believable, but is it a good thing? It may be if we want the things that unsupervised teenagers pick up from a radically commercialized and bureaucracy-ridden environment to be the basis of our national way of life, but perhaps not otherwise.