Roger Federer said he will donate $500,000 to aid children affected by the war in Ukraine, while the United States Tennis Association (USTA) said it would donate a percentage of ticket revenue from their Billie Jean King Cup tie against Ukraine to a relief fund. The U.N. Refugee Agency (UNHCR) said earlier this week that nearly 3 million refugees have fled Ukraine, about 7 percent of the country’s population, since Russia’s invasion began on Feb. 24. “My family and I are horrified seeing pictures from Ukraine and heartbroken for the innocent people who have been so terribly affected. We stand for peace,” Federer said on Twitter. “We will provide assistance to children from Ukraine who need care, about 6 million Ukrainian children are currently out of school and we know it’s a very critical time to provide access to education and would like to support them to deal with this …