How to store file descriptor in a struct

Question

I have a program which spawns multiple children. The number of children spawned is unknown as it relies on user input. Every child and parent must have two pipes connecting to them. However, I want to access the file descriptors of the pipes to be able to read and write to the specific child using the pipes in future functions. I have looked into making the file descriptor as fd[i][2], i being the specific child that pipe is referring to. I am aware I will have to dynamically allocate the file descriptors as the array is increasing in size every time the user creates a new child. I know that every child will have an array being fd[2][2]. My goal is to store the file descriptors in a struct so I can access them in other functions. But I am struggling with how to allocate the memory for the file descriptors. I don't really have code to show as it is more of a knowledge-based question. What I have is a struct:

typedef struct {
    int* fd[2][2];
}FileDesc;