BEIRUT—Rising food prices as a result of the Russian invasion of Ukraine are increasing the risk of malnutrition of millions of children in the Middle East and North Africa, the U.N. children’s agency warned Thursday. UNICEF added that families are struggling to put food on the table during the Muslim holy month of Ramadan, when observant Muslims abstain from eating and drinking from sunrise to sunset. Countries in the Middle East and North Africa have been hard hit by wars and poverty and the coronavirus has only made things worse. Russian troops began invading Ukraine on Feb. 24, and since then, intense fighting in different parts of the country has disrupted food exports. Since the invasion began, Western countries have imposed crippling economic sanctions on Russian institutions. Ukraine and Russia account for a third of global wheat and barley exports, which countries in the Middle East rely on to feed …