Macmillan Cancer Relief, St Giles Trust, and Hope and Homes for Children are to share £525,000 from Lloyd's Charities Trust.
The charities were chosen after a "rigorous" selection process and the money will be distributed toward specific projects over three years.
Hope and Homes will get £75,000 each year towards assisting vulnerable children in Sierra Leone. Hope and Homes was chosen as Lloyd's Charities Trust's 50th anniversary charity.
Lloyd's is also raising a further £35,000 a year from the insurance market to help the project find families and provide healthcare, education and micro-finance support to children, many of whom have lost parents to war and HIV.
Macmillan will use its annual £50,000 award to help its national Cancer Line service that targets children and BME groups.
St Giles Trust will use its annual £50,000 to create a peer adviser programme for 4,000 children.