可以使用AutoMapper提供的自定义解析器来解决这个问题。下面是代码示例：

首先，我们需要定义一个自定义解析器：

public class CustomResolver : IValueResolver
{
    public ChildDestination Resolve(Source source, Destination destination, ChildDestination destMember, ResolutionContext context)
    {
        // implement your custom logic here to map properties from Source to ChildDestination
        return new ChildDestination();
    }
}

然后，在配置映射时，我们可以使用这个自定义解析器来映射ChildDestination类型：

// configure mapping from Source to Destination
var configuration = new MapperConfiguration(cfg =>
{
    cfg.CreateMap()
       .ForMember(dest => dest.Child, opt => opt.MapFrom(src => src.ChildDestination))
       .ForMember(dest => dest.AnotherChild, opt => opt.MapFrom(src => src.AnotherChildDestination));
});

// configure mapping from ChildSource to ChildDestination using custom resolver
configuration.CreateMap().ForMember(dest => dest.ChildProperty, opt => opt.MapFrom());

// create a mapper
var mapper = configuration.CreateMapper();

// use mapper to map objects
var source = new Source();
var dest = mapper.Map(source);

这样一来，当我们在映射中遇到ChildDestination类型时，就会自动使用我们定义的自定义解析器来进行属性映射。您可以通过重复配置CreateMap方法来配置多个自定义解析器，每个自定义解析器都适用于不同的子类型。