A growing number of children haven't received any vaccinations by the time they turn two, the Washington Post reports.

By the numbers: The number of unvaccinated children is still small, but public health experts are still concerned by the fact that it's growing. The percentage of unvaccinated children has quadrupled over the past 17 years, according to the Post. There are now an estimated 100,000 children younger than 2 who have never received any vaccinations.