How to implement C++ class heritage properties in C using C struct?

hi,all,
I have a C++ program need to convert to c language to be used in a
emabedded system. the problem is that the original code was writtern
in C++ language with Parent class and some child class. How can I
invert these C++ code into pure c code by using struct in C language?

Can somebody give me any ideas? thanks.

For example, how to conver the following code into pure c code?

class PARENT
{
public:
	virtual int Init();
	virtual int Add();
	virtual int Sub();
	int 	Otherfunc();
	
private:
	int x;
	int y;
	int z;
};


class CHILD1: public PARENT
{
public:
	int Init();
	int Add();
	int CHILDOwn();
privete:
	int a;
	int b;
	int c;
};

class CHILD2: public PARENT
{
public:
	int Init();
	int Add();
	int Uncle();
privete:
	int m;
	int n;
	int d;
};

PARENT* CreateNewInstance()
{
	PARENT* pPointer=new CHILD1;
	return pPointer;
}

main()
{
	PARENT * Kids1=CreateNewInstance();
	Kids1->Uncle(); //from children class
	Kids1->Sub();   //from parent class
	Kids1->Otherfunc();//from parent class
}