Prometheus' actress Charlize Theron took her son Jackson to a children's gym in West Hollywood, California on February 12, 2013.
Jackson celebrated his first birthday earlier last month superhero-themed party at the Coop, a fun space for kids in L.A.'s Studio City.
"It was a really mellow party," a source tells Us Weekly of the celebration, which was attended several celebrities and their kids. "Charlize is the nicest person on earth. She's gorgeous and relaxed and sweet."
"Charlize absolutely adores [Jackson]. They have the most wonderful relationship," the insider adds One sweet example of her maternal instincts? "[Jackson] was jet-lagged, so when everybody sang 'Happy Birthday,' they had to whisper it. She didn't want it to be really loud."