"We r so proud!! Romeo ran London mini Marathon for UNAIDS and 7 Fund x vb," mom Victoria posted on Instagram early Sunday. "Well done Romeo!!" she wrote in a second post.
She and David Beckham, plus Romeo's brothers Brooklyn and Cruz, were waiting after he crossed the finish line.
Romeo's run was in support of the Joint United Nations Programme on HIV/AIDS and the "7" fund, a collaboration with UNICEF providing assistance to children in danger zones around the world, according to Victoria's posts.
Romeo seems to be following in his dad's footsteps: David said earlier this year that the fund was his "number one priority."