Well these are all good suggestions, but I am truly shocked that no one has mentioned BIZ. Recommended to me by a Duke Chemistry Dr., BIZ is THE MOST AWESOMEST THING EVER!!! For organic stains, it has no equal. Grab a cheapie mop bucket, a cup of Biz and let it sit for 2-3 days (yes, days...). It takes out pee, poo, grass, food, blood, formula and DIRT. If it's organic, this stuff works like a charm!! Whites are white as can be.
I have soaked my socks in a bucket of lemons (acid goes to work), but with a large family, I just keep a bucket in my laundry room and let things soak in Biz for a few days. I have passed this wisdom on to many a happy friend who stocks Biz for these emergencies. Good luck!