He also might have picked up a bit of a bug, because that can make the poos green. He might not have been symptomatic, becuase his body may have fought off the bug (hence the green poos ).

Jessalyn has green stringy poos when there is excess bile being dumped from her liver, so I know that bile dumps look green, glugy and stringy - but that wouldn't be the cause of Cole's green poos - unless he had been in contact with some kind of toxin or something that was processed by the liver making more bile than usual.
Mmm, his older sister Lucy wa really sick last week with an ear infection & UTI, maybe he got something from her?

Someone else just mentione ot me that green poo indicates an excess of iron, which I'm not sure about cos I usually have an iron deficiency...