Usually broken or choppy family-use Chinese, of whatever dialect the parents speak in the house. Same holds true for most other ethnic backgrounds, such as Vietnamese or Peruvian.
Chinese language schools used to suck really bad. They suck less now but you can’t really improve proficiency without practice and that is usually a function of interest. That depends on the individual and their circumstances. There is also a social intimidation factor wherein speaking Chinese gets you cold stares, or worse.
But yes, at least one ABC speaks Chinese. That much I can vouch for on a personal basis.