How do I store downloaded textures in a list and use them?

So I have downloaded a few images and I would like to put them in a List of textures. As below:

WWW www = new WWW(url); yield return www;

www.LoadImageIntoTexture(texture); textures.Add (texture);

'textures' is the list that I'm adding the images into.

But when I do this:

FileButton.transform.GetChild (0).GetComponent().texture = textures[i];

It says Argument out of range.

I'm fairly new to this so any help would be appreciated.