The 31-year-old actress spent some quality time with the 45-year-old Tesla founder and his sons Tuesday at Sydney Opera House in Australia.
"Kidding around," she captioned a series of photos from the outing on Instagram.
Musk shares twins Griffin and Xavier and triplets Damian, Kai and Saxon with first wife Justine Musk. He and Heard were first linked in 2016 after splitting from their respective spouses, Talulah Riley and Johnny Depp.
"Sydney is such a beautiful city," the entrepreneur captioned a picture of himself with Heard and one of his sons.
Heard and Musk were all smiles during a date night Sunday in Sydney. Sources told People this month that the Tesla founder has seemed "noticeably happier" since he started dating Heard.
"Elon and Amber are already very serious about each other," an insider said. "She spends a lot of time at his house and is very comfortable there. Amber's also gotten to know his kids and spends time with them as well."
Heard filed for divorce from Depp in May 2016 after alleging the actor was abusive during their relationship. She will next star in London Fields, and will play Mera in Justice League and Aquaman.