Toddlers diarrhea where greenish undigested particles are passed is quite common among young kids.
It is due to high
sugar, high fibre or low fat diet.
Avoid high sugar beverages or very sugary fruits for the time being.
However Passing loose stools, more than thrice a day, foul smell, blood in stools or being dull or passing less urine is worrisome. If so do consult a pediatrician.