public class ParentClassOne {

    protected String someValue1;
    protected String someValue2;

    protected ChildClassOne itemOne;

    public ChildClassOne getItemOne() {
        return itemOne;
    }

    public void setItemOne(ChildClassOne itemOne) {
        this.itemOne = itemOne;
    }

    ...setter and getter methods for the rest of fields...
}

public class ParentClassOne {
    ...this class contains the same elements like the first one...
}

ModelMapper modelMapper = new ModelMapper();
modelMapper.getConfiguration().setMatchingStrategy(MatchingStrategies.STANDARD);
modelMapper.getConfiguration().setMethodAccessLevel(AccessLevel.PUBLIC);
modelMapper.getConfiguration().setFieldAccessLevel(AccessLevel.PROTECTED);

info.p2.ParentClassOne result = modelMapper.map(data, info.p2.ParentClassOne.class);

public ChildClassOne {
    protected List<ChildAnyClass> children;

    ...getter method...
    Notice: ...there is no setter method for the list....
}

ModelMapper modelMapper = new ModelMapper();

Converter<ObjectOne, ObjectTwo> converter = new Converter<ObjectOne, ObjectTwo>() {
    public ObjectTwo convert(MappingContext<ObjectOne, ObjectTwo> context) {

        ObjectTwo dest = new ObjectTwo();
        if (context.getSource() != null) {

            // Converts list from source object into the list of destination object
            Type listType = new TypeToken<List<ObjectTwo>>() {}.getType();
            List<ObjectTwo> items = modelMapper.map(context.getSource().getList(), listType);

            dest.getList().addAll(items);
            return dest;

        } else {
            return dest;
        }
    }
};

modelMapper.addConverter(converter);