A source tells ET that the two stars planned the family vacay for a time when Kate's sons, Bingham and Ryder, were out of school, and that Muse frontman Matt Belamy -- Kate's ex and Bing's dad -- joined them on the trip. Matt kept an eye on the kids, giving the girls a chance to play in the surf.
Along for the vacation were Kate's besties, stylist Sophie Lopez and Kari DeLonge.
Goldie Hawn & Kate Hudson flaunt their amazing beach bods in Greece
PARIS, FRANCE - JANUARY 25: (L-R) Goldie Hawn, Donatella Versace and Kate Hudson attend the Versace show as part of Paris Fashion Week Haute Couture Spring/Summer 2015 on January 25, 2015 in Paris, France. (Photo by Pascal Le Segretain/Getty Images)
BEVERLY HILLS, CA - NOVEMBER 21: Host Goldie Hawn (L) and host committee member Kate Hudson are seen onstage at Goldie Hawn's inaugural 'Love In For Kids' benefiting the Hawn Foundation's MindUp program transforming children's lives for greater success at Ron BurkleÂs Green Acres Estate on November 21, 2014 in Beverly Hills, California. (Photo by Jason Merritt/Getty Images for The Hawn Foundation)
BEVERLY HILLS, CA - NOVEMBER 21: (L-R) Matthew Bellamy, and actresses Goldie Hawn, and Kate Hudson attend Goldie Hawn's Inaugural 'Love In For Kids' Benefiting The Hawn Foundation's MindUp Program at Ron Burkle's Green Acres Estate on November 21, 2014 in Beverly Hills, California. (Photo by Frederick M. Brown/Getty Images)
BEVERLY HILLS, CA - NOVEMBER 21: (L-R) Actress Rosanna Arquette, host Goldie Hawn, host committee member Kate Hudson, and emcee Kathy Griffin attend Goldie Hawn's inaugural 'Love In For Kids' benefiting the Hawn Foundation's MindUp program transforming children's lives for greater success at Ron BurkleÂs Green Acres Estate on November 21, 2014 in Beverly Hills, California. (Photo by Michael Buckner/Getty Images for The Hawn Foundation)
CULVER CITY, CA - NOVEMBER 08: (L-R) Actors Goldie Hawn, Kate Hudson and Kurt Russell attend the 2014 Baby2Baby Gala, presented by Tiffany & Co. on November 8, 2014 in Culver City, California. (Photo by Amy Graves/Getty Images for Baby2Baby)
London, UNITED KINGDOM: US actress Kate Hudson (L) with her mother Goldie Hawn, arrives at the London Premiere of her film , Skeleton Key, in London's Leicester Square, 20 July 2005 AFP PHOTO MAX NASH (Photo credit should read MAX NASH/AFP/Getty Images)
HOLLYWOOD - MAY 26: Actress Goldie Hawn (left) and her daughter, actress Kate Hudson attend the film premiere of the romantic comedy 'Raising Helen' on May 26, 2004 at the El Capitan Theatre, in Hollywood, California. (Photo by Vince Bucci/Getty Images)
NEW YORK - MAY 1: Actress Goldie Hawn (left) and daughter Kate Hudson arrive at the 'Raising Helen' screening during the 2004 Tribeca Film Festival on May 1, 2004 in New York City. (Photo by Evan Agostini/Getty Images)
370672 07: Award hosts Goldie Hawn and Kate Hudson arrive at the 'Women in Film's Annual Crystal Awards Luncheon at the Century Plaza Hotel in Century City, CA on June 9, 2000. (Photo by Chris Weeks/Liaison)