My Cellphone pictures

Week ago my oldest son borrowed my 8 gig micro disk from my cellphone instead buying a new one that I let him used it. I have lots of pictures on my disk that I'm using it to my cellphone. Before I let my son use it I asked my daughter if she knows how to download, she said Yes. I didn't check it out until a week my son came back from Utah, just notice that lots of pictures was missing when my daughter download, so i thought maybe still left some of the files on the disk. I waited my son to return the disk back to me and I checked so many time if the rest of the pictures was somewhere on the files but never found it. I'm so upset that all the pictures that I had it's gone, do not know what happen. Their were more than 300 pictures but only 17 was download. No matter how I back and forth to look for the file not there, maybe somehow it got delete it before transferring the files. The memories of the pictures I had on the disk it's all gone, gone, gone!