SAN DIEGO (AP) — A U.S. official says the number of children traveling alone who were picked up at the Mexican border by U.S. immigration authorities likely hit an all-time high in July. Preliminary government data released Monday by a Department of Homeland Security official also says the number of people who came in families likely reached its second-highest total on record. The sharp increases from June are especially striking because crossings usually slow during stifling summer heat. The disclosures came in a court filing hours after immigrant advocacy groups resumed a legal battle to end the government’s authority to expel families at the border on grounds it prevents the spread of the coronavirus.