Ditto! I opened mine last week and was gutted that all my gorgeous wee white clothes had yellow stains on them. I had washed them and packed them up really well I thought but Mum thinks it is the acid (or whatever) in baby sick that can do it.
The good news is that mine have been washed and look like new again!

Mum helped me (she is a star washer!) and made a paste with nappi san oxiaction and put on the stains. Then washed them with nappisan. They look really good.
Am sure yours will come out too.