Kitten smells bad

[Jane25788]

Hey my kittens are 3 weeks old mum is still here the kittens really smell I lost 1 yesterday to fading kitten syndrome we have 2 left but they stink I rang the vets today and they said if it's eating well from mum and moving ok then it should be fine but after losing 1 I'm worried is it.normal for 3week old.kittens to really smell bad