Editor's Note: "Henrietta Fore is the executive director of UNICEF. The opinions expressed in this commentary are solely those of the author. View more opinion on CNN. "

(CNN)When the Covid-19 pandemic began sweeping across the planet, there was a lot the world did not know about its impact on children. Could they get sick? Could they transmit the virus? Were schools safe?
We have since learned quite a bit. We have learned that children are not the main drivers of the epidemic across countries.

Meanwhile, we know there can be severe negative effects on children -- from deterioration of mental and physical health to lack of sufficient food in some cases -- when they are out of school. It is now clear that children -- and the world at large -- would be best served if schools reopen.
We must first ask why many schools around the world are still closed?

Strict measures were taken to help contain the spread of Covid-19 and flatten the curve. Often, schools were among the first places to close, sometimes even before shopping malls, movie theaters and restaurants. By early April, nation-wide lockdowns in 194 countries left 1.6 billion children out of school, approximately 90% of the world's students. As of today, two months on, while many countries begin to ease lockdowns for non-essential services, over 1 billion children in 144 countries are still not in their classrooms. These are not children home for summer vacation -- they are students whose educations have been disrupted. ......