I received a lot of hand me down baby clothes from my sister and SIL. I noticed a lot of the ones from my SIL have yellowed stains on the neck and chest, while my sister's didn't-- I am taking a guess here but does formula stain a lot worse than breast milk? Sister breast fed and SIL formula fed, so that's my theory.

My real question is, is there any way to remove the yellowed stains from clothes that have been stored for about 2 years? I am not going to be too fussy about it-- a onesie to go under an outfit doesn't need to be spotless, but at the same time, would be nice if it didn't look totally dirty. Any brilliant solutions?