My 9 week old kitten is pooping every wheres plz help?

i got a new kitten bout 2 weeks ago from ppl who had about 9 other cats and they also had his brothers and sisters.. they said he was litter trained.. i put his box in the bathroom showed him where it was then he started pooping in the livingroom i would clean it up and take him to his box and everytime i see him go to that corner i would pick him up and put him in the box now he is pooping under my bed in the hallway, kitchen, my kids room but sometimes uses his box how do i get him to stop he is messing up my carpet and i rent i dont wnat to get rid of him but i cant have him pooping every wheres it smells and its nasty... i tryed lockin him in one room but he crys for hrs if he isnt with anyone...also he has had diarrhea i was told it was the most cat food so i switched but it dosent seem to help. plz help me im at my last string here