kittens pooing...

[destiny22]

ive had my kittens who are 10 weeks old for only a week,they both came from same litter and both female but one of them constantly poos after eating while the other is fine,its as though its going straight through her and shes always hungary still. the previos owner didnt worm them and i was wondering if this is what is causing it..plus its stinky big style...