While child mortality rates are declining each year, we've still got a lot of work to do. In a new video, Melinda Gates speaks out on three things that she says could help save millions of children — family planning, breast-feeding, and vaccines. Gates discussed the importance of contraceptives and family planning, explaining, "If every woman who didn't want to become pregnant had access to contraceptives, infant mortality would go down by 1/5." That's why, she says, she's been an active advocate of making sure that women have access to birth control, pledging to help 120 million women have access to contraception by 2020. She also stressed the benefits of breast-feeding in providing infants with the necessary nutrients for their healthiest lives, and advocated for the importance of vaccines in saving children's lives. All in all, Gates said, "One of the things humanity should be the most proud of is the number of children's lives that we have saved. We know how to save more, and the question is, will we?" According to the World Health Organization , 5.9 million children under the age of five died in 2015 due to conditions that could have been prevented or treated. "Reducing childhood mortality is the heart of the work for us," Gates said in the annual letter that she and her husband, Bill Gates, wrote to Warren Buffet. "Virtually all advances in society — nutrition, education, access to contraceptives, gender equity, economic growth — show up as gains in the childhood mortality chart, and every gain in this chart shows up in gains for society."