"What did these children do to deserve this? This summer share a thought for the innocent lives lost every day in war," he wrote alongside the photos.
The Herald has chosen not to republish the photos. Williams has had a mixed response to the images of two young boys, wounded and dead in what appears to be a street.
Other celebs who have used their profile to promote a cause:
David Pocock of Australia speaks to the media during an Australia media session. Photo / Getty
Australian rugby player David Pocock is a vocal supporter for same-sex marriage rights. The former Wallabies captain has spoken out against homophobia in rugby and sport and has said publicly he will not marry his long-time partner Emma until there are equal marriage rights for gay people in Australia. Pocock is also a staunch climate change activist and was arrested last year for chaining himself to a digger outside a coal mine to show solidarity.
Basketball legend Michael Jordan in his prime. Photo / Supplied
American NBA legend Michael Jordan is well known for his involvement in charities including the Boys' and Girls' Clubs of America, UNCF/College Fund, Special Olympics and a number of other charitable organisations that support children and families. In August he donated to charity $8.9 million he won in a lawsuit against a grocery chain that used his image without his consent.
Jonah Lomu at the 'Stand In Black' campaign launch. Photo / Supplied
The late Jonah Lomu was a big man with a big heart. He was heavily involved with Kidney Kids New Zealand and Unicef. He became a Unicef ambassador four years before he died and said he wanted to do his best to help other disadvantaged children around the world. In 2012, Jonah lived on no more than $2.25 a day as part of a Global Poverty Project initiative. The education and campaigning organisation aims to increase the number and effectiveness of people taking action against extreme poverty.
Dan Carter, the former New Zealand All Black. Photo / Supplied
All Black Dan Carter, surfer Paige Hareb and Silver Fern Maria Tutaia are ambassadors for Canteen, a charity that supports young people living with cancer in New Zealand. All are involved in the annual bandanna day fundraiser, and have in the past designed a number of patterns for the cause.
LA Galaxy football player David Beckham talks to the Media during a press conference with the LA Galaxy and the Oceania All-Star team. Photo / Supplied
David Beckham is also a Unicef ambassador. The football superstar also lends a hand to the Unite Against AIDS Campaign and set up a charity with his wife, the Victoria and David Beckham Charitable Trust, which gives children wheelchairs, among other causes.
Tennis great Serena Williams. Photo / AP
Tennis great Serena Williams has received a number of awards for her charity work. She is involved with the Avon Foundation, which focuses on breast cancer. Williams is also a Unicef Goodwill Ambassador, and in the past travelled to Ghana to advocate for better education for children in the developing world.
World number one golfer Tiger Woods, at a press conference in Auckland, New Zealand. Photo / Supplied
Golfer Tiger Woods runs the Tiger Woods Foundation, which provides education for underprivileged youths. The foundation's programmes aim to break the cycle of poverty through college-access opportunities for low-income students. Named after his father, the Earl Woods Scholarship Programme runs alongside the foundation providing college scholarships and a support system including mentors, professional development workshops and internships.
World champion shot putter Valerie Adams with Year 1 and 2 students getting active at the Rotorua Village Green. Photo / Supplied
Olympian Valerie Adams, All Black Israel Dagg, Black Caps skipper Brendon McCullum, Warriors player Shaun Johnson and Silver Fern captain Casey Kopua have put their names to a Government-funded anti-obesity campaign. The stars are appearing across various media to promote the message "Big change starts small".
