Dynamic array of structs containing a dynamic array of structs

I can't for the life of me figure out how to solve this in c.

I have the following structs:

typedef struct
{
    uint8_t         index = 0;
    DLPageItem_t    *pageItems = NULL;
    uint8_t         pageItemCount = 0;
    uint8_t         selectedItemIndex = 0;
} DLPage_t;

typedef struct
{
    uint8_t         index = 0;
    void            *valuePtr = NULL;
    uint16_t        tmpValue = 0;
    DLItemType_t    type = DLITEMTYPE::NOTYPE;
    uint8_t         row = 0;
    uint8_t         col = 0;
    uint8_t         targetPageId = 0;
    DLItemAction_t  action = DLITEMACTION::EDIT;
    bool            selectable = false;
    bool            editing = false;
} DLPageItem_t;

And I want to have a dynamic array of DLPage_t (with realloc) and then be able to anytime add DLPageItem_t to any of the already created DLPage_t array members.

So I tried to have a

DLPage_t *_pages = NULL;

and do

this->_pageCount++;    
this->_pages = (DLPage_t*)realloc(this->_pages, this->_pageCount * sizeof(DLPage_t));

Then I'm accessing the "pages" and setting the values like this:

this->_pages[this->_pageCount - 1].index = this->_pageCount - 1;

The function which adds DLPageItem_t structs to a DLPage_t struct member, I do it like this:

this->_pages[pageId].pageItemCount++;
    this->_pages[pageId].pageItems = (DLPageItem_t*)realloc(this->_pages[pageId].pageItems, this->_pages[pageId].pageItemCount * sizeof(DLPageItem_t));

I have some very funny business going on so I guess I'm doing something wrong and accessing/overwriting memory where I shouldn't.

Can someone please verify whether what I'm doing is correct? I tried to apply/adapt this to my issue but I just can't figure it out: https://stackoverflow.com/a/15397992

Thanks!