Yes, calm down sweetie. It's not as nearly as bad as it seems to find blood in their poo. It usually indicates a food sensitivity ... namely, dairy. Especially in green, mucousy stools.
Dr. Jay Gordon says:
Red streaked stools
This usually comes from bleeding in the lower intestine or rectum. Most often it is caused by rectal fissures which are tiny "cuts" around the circumference of the anus. This can be a reaction to dairy in mom's diet. Elimination of all dairy is the first line of defense in this situation. I have seen countless babies who had blood in their poop which resolved when mom stopped all dairy products and returned with even a small amount of milk or cheese. Other dietary changes may be needed for breastfeeding moms. Formula fed babies lose blood from the lower intestine when they drink cow milk formula and some have the same losses on soy formula. Occasionally, this "micro-hemorrhaging" can become visible as blood streaking on the surface of the stool. Persistent or increasing blood in the stool or blood mixed with mucus (described as "currant jelly" stool in the texts) requires an immediate call to your doctor.