a really good soap for cleaning is called “fels naptha” it has been around forever, but may be a little hard to find. i have had a store order it in for me before. it is a bar soap and you use it to hand scrub. it is pretty amazing stuff.
here’s a trick my mom taught me for black grease stains—i know it’s not baby poop, but i thought it might come in handy for someone. you rub shortening into the black grease—this will break it down—and then you use the fels-naptha to get the greasy residue out. i used this trick once on a white shirt of kevin’s that had had some greasy stuff he had used to preserve wood. it had been on his shirt for probably a year—-and i was able to lighten the stain a considerable amount even after that long.