Generation Z, or the post-millennial generation, are only barely a majority white, according to new Census Bureau estimates of the U.S. population that include details on race and ethnicity.

Kids 15 and under are 49 percent minorities, according to the figures released Thursday by the bureau, which called them part of the "most diverse generation."

The youngest cohorts are majority-minority: Babies who hadn't yet had their first birthday were 51 percent minority. That was true for all the ages up to 5.

The post-millennial generation, at nearly half minority, is significantly more diverse than millennials, who are 55 percent non-Hispanic white.

Generation X, in turn, is just under 60 percent non-Hispanic white, while the Baby Boom generation is 72 percent.

Although there are no widely agreed-upon definitions for the different generations, the bureau counts millennials as those born between 1982 and 2000 and baby boomers as those born between 1946 and 1964.

The growing Hispanic population drives many of the overall demographic changes in the U.S. The Hispanic population increased by 1.2 million, or 2.2 percent, between 2014 and 2015, to 56.6 million. Most of that growth was the result of births rather than immigration.

The fastest-growing minority group was Asians, who saw their numbers increase by 683,000, or 3.4 percent, to 21 million, thanks mostly to migration.