The boy didn't make if very difficult to find him. He'd made a febble attempt to attack him, but Grindelwald blocked it again. "Accio Wand," he muttered in order to collect the boy's wand. Just so he wouldn't be ever more difficult.
"Petrificus Totalis," he said aiming at the boy's less than convenient hiding spot. They needed to be out of there quickly, and he still had to get Ariana. Once he was sure the boy was immobile, he made James float behind him, as Grindelwald quickly made his way to the edge of the Forbidden Forest where Ariana would be waiting.