The girls and their family have always been close to the Gibsons and the former couple agreed to make a rare public appearance together to spend their birthday celebrations with them.
Gibson told People.com, ""We're all involved in Josie and Teresa's lives. It's incredible seeing Josie and Teresa do so well. Listening to Josie speak, you think, 'Man, this is the happiest kid I've ever seen.'""
They briefly bonded as they played with their five-month-old grandson at the Hawaiian-themed party.
According to the website, the former couple was later honoured for their support of the Mending Kids charity, which provides life-changing surgical care for children worldwide.
Robyn was the president of the organisation's board of directors and Mel recently returned from two Mending Kids trips to Guatemala and Panama.