There are a number of things that can be done:

Laws and Regulations
International and national laws help give authorities the right to convict people who treat child workers badly.  Other laws can make it illegal to bring children into the country for work or protect children who have been trafficked into a country.  Many companies based in the industrialised world have now adopted codes of conduct intended to stop children below 15 from being involved in manufacturing goods that the company imports from developing countries.  If you have any big companies in your region you could write to them to see what their policies are.

Education

Children can be educated about their rights and where to get help if they need it.  Educating child labourers can also improve their skills and help them improve their circumstances for example, if they can count and keep track of the number of bricks they have smashed they have a better chance of being paid for the correct number.  The public can also be educated about the effects of child labour on children and encouraged to support fair trade goods.  People who employ children can be educated about how treating the children well (e.g. allowing them to go to school) will also improve the work the children do.

Attitude

To challenge popular attitudes and prejudices that result in abuse, and encouraging the media and general public to confront exploitation, abuse and violence.  Encouraging local communities to consider the maltreatment of children as unacceptable.  There are many ways to do this such as performing dramas in communities which highlight the abuse which happens behind closed doors.

Poverty Reduction

Reducing poverty will mean parents aren't forced to send their children to work or sell them to employers in order to survive.  This can be done through helping train adults in skills needed to improve their income (especially women as they mostly care for children).  NGOs (Non-Governmental Organisations) come alongside communities to support them in a number of ways, such as helping with medical care, providing basic food resources, housing, protecting children from abuse, digging wells etc.  All of these things reduce the financial and physical strain on families and individual children.