Both Unicef ambassadors, the retired footballer and singer, are fronting a new UK campaign by the organisation to safeguard children from violence, disease, hunger and the chaos of war and disaster.
In separate images, they are pictured holding out their hands in front of the shadows of unidentified minors.
Earlier this week, Unicef released a report that highlighted the epidemic of violence facing children in the modern world.
Entitled "Children in Danger: Act to End Violence against Children", it revealed that every five minutes a child around the globe dies as the result of violence. It also estimated that some 345 children under the age of 20 could die from violence each day in the next year, unless governments act.
Beckham said: "If you saw a child in danger, any child you would instantly step up and protect that child from whatever threat they were facing.
"Millions of children around the world are facing dangers every day - violence, disease and disasters. We need to grab this opportunity to step up and protect them now."
"I’ve met children around the world who are facing all kinds of dangers – kids in Haiti who lost everything in the earthquake and little children in Mexico at risk of violence and abuse," Williams added.
"Since becoming a dad I realise more than ever how much these children need someone to protect them."
Beckham has four children with wife Victoria, while Williams is expecting his second child with wife Ayda Field. His single “Go Gentle” is dedicated to his daughter Teddy.
Unicef UK’s Children in Danger campaign calls for a target to end violence, exploitation and abuse of children to be included in the world’s new development agenda in 2015.Reuse content