Stains

Is there anyway I can get old spit up stains out of a white shirt?? It was my sons outfit when he was a baby and I love it and want my new baby to wear it... However my son had acid reflux and spit up a lot. Its such a cute outfit and I kept it because I love it so much lol. I didn't realize it was stained until I got some of my sons baby stuff out preparing for the new baby