action body_action()
action child_action()

ENTITY* body = ent_create(body, pos, body_action);

//main body action
action body_action()
{
   //msc codes here
   code...

   //create child entity
   ent_create(part1, pos_parentoffset, child_action(me)); //point me as parent entity

   //rest of the child entity code
   code...
}

//child body action
action child_action(ENTITY* parent_ent)
{
   //msc codes here
   code...

   while(1)
   {
       //parent_ent pointing to main body
       vec_set(my.x, parent_ent.x);
       wait(1);
   }
}

//main body action
action body_action()
{
   //msc codes here
   code...

   //create child entity
   ent_create(part1, pos_parentoffset, child_action); //point me as parent entity

   //rest of the child entity code
   code...
}

//child body action
action child_action()
{
   //msc codes here
   code...
   ENTITY* parent_ENT = you;

   while(1)
   {
       //parent_ent pointing to main body
       vec_set(my.x, parent_ent.x);
       wait(1);
   }
}