The cat eating the kittens if you touch them thing is a myth. The only times a cat might eat their kitten/kittens is if they're extremely stressed, malnourished, or if a kitten is ill or dies. And even in those cases it's still rare and the cat is more likely to abandon the kittens rather than eat them. A cat may decide to move her kittens and try to hide them if she doesn't like them being handled, but that's about it. And lots of cats actually like when their kittens are handled by humans for various reasons, so it's possible she won't have any issue with it regardless.

I'm not sure where the myth came from, but my guess is that in rare cases some feral cats or new mothers get so stressed by humans handling their kittens too much that they eat the kittens because they feel like the environment isn't safe enough for raising a litter and go nuclear, but I doubt this happens often even among cases of cats eating their young, and like I mentioned before the cat is far likelier to abandon the kittens rather than eat them unless she's starving. A cat isn't going to lose the ability to recognize their kitten just because they have human scents on them. They use more than just their sense of smell to recognize their kittens, and handling a kitten isn't enough to completely remove the kitten's smell. Cat's noses are too sensitive for that. Not to mention if that was all it took to get a mother to reject their kitten, then it wouldn't be so common for mother cats to adopt kittens that they didn't give birth to, or even baby animals from a different species. Their mothering instinct post-pregnancy is too strong for something like scent to be a primary factor.

Many flea treatments can be unsafe for newborn kittens because of how sensitive they are, so don't cover them in any mixtures you read about online without consulting a vet first. Don't use soap on them either, and submerging them in water isn't a good idea. I think the usual method for kittens that young is just using a very fine flea comb and dampening their fur with warm (but not too hot) water, then picking off the individual fleas by sight, since they're small enough for that method to be effective. Even if their fur is dark, the flea comb and a good light source can still allow you to see and pick them off effectively, and the water will cause them to gather in the drier spots, making them easier to find. Then you let them dry in a warm place to make sure they don't get too cold after. Kittens can be very sensitive to changes in temperature which is part of why bathing them outright isn't a good idea, and why keeping them warm after dampening their fur is important. Also you'll want to treat the mom at the same time, so she doesn't just give the fleas to the kittens again, and clean all their bedding and whatever their bedding is kept in (if they're in a box for example).

I highly recommend calling a local vet to ask over the phone about what methods to use to de-flea both the mother and the kittens, at the very least. Even better if you're willing to get them an appointment, the sooner the better since fleas can be dangerous for young kittens, even if you don't think they have many on them. The mother can probably be medically treated, but the kittens can't. Whatever source you're getting this "I read" info from isn't reliable, and while I try my best to do my research, I'm not a vet, I'm just a random person on the internet. so I would recommend consulting a professional first and foremost if you want to be absolutely sure that what you do is safe and won't hurt the kittens. Even if you don't want to pay for an appointment, most vets are willing to answer questions and give advice over the phone. Source: I worked at a pet hospital and often consulted the vets about questions asked over the phone.