7 day old kittens smell

My cat gave birth 7days ago to 6 kittens and the first towel i used cover in yellow and smelled bad, saw it once the mother moved her kittens away and she didnt want to go back in there as it was disgusting, now shes taking them behind my bed and im not sure what to do they still smell, would she groom each one of them any time soon? need some advise guys, should i leave her to it or should i step in ? cheers thank you   

Covered in yellow? Sounds like the mother possibly has an infection or is she not cleaning up the kittens poop?

Bedding needs to be changed twice a day to begin with, if it's not been touched for 7 days of course she moved her kittens away. If she's not taking proper care of the kittens you will need to step in, use a damp flannel being extremely careful not to chill the kittens.