Kittens nursing on each other

I have two, 8 week old foster kittens. They were with Mom up until this weekend when she went back to the shelter to be spayed. Before she left they were both completely switched to solids and she was not allowing them to nurse at all. The past two nights I have noticed one trying to nurse off of the other. He's not going for her genitals, which I think is more common, but actually trying to nurse. The obvious assumption is he misses Mom but she's still recovering. My question is has anyone else experienced this behavior (it's a first for me) and if so, should I try to prevent it or will he grow out of it? Nothing else has changed: they are in the same living environment they were born in. I looked at some other websites and saw conflicting reviews: some said let it run it's course, others said separate them right away, even to the point of putting something non-toxic but not good tasting on the nursor's nipples to discourage the nursee, though I have no idea on what that substance may be and don't want to discourage her from grooming herself. Thoughts? 

Thanks! 

Not clear if mum is coming back or not.  The friends whose cats have had sections (far more traumatic than a spay) have usually got striaght on with nursing their new kittens once round from the anasthetic, so not sure why mum is still recovering unless there were problems.

If he is suckling on her, he may move down to to other areas. We have three little boys in danger of losing their ability to urinate because they were so badly suckled on.

We use Bitter Apple to keep them from suckling on each other, but it does need to be reapplied. So far it seems to be working!

We have had no problems with the boys not trying to groom themselves, they just tend to avoid the area with the bitter apple. Hopefully once mom has recovered, the boy will stop.

Sorry I didn't explain that well as I was trying to avoid the dramatic version but I'll tell it anyway. Usually, the kittens and Mom go back to the shelter together and all have their surgeries at the same time and go up for adoption. The shelter I am with did not inform me of a policy change when I took this litter that they now want Mom's back once the kittens are weaned but want the kittens to stay in foster until they reach a minimum of 4 pounds (this is the very short version on a very long drama). I have advocated for juvenile (8-12 weeks) spay/neuters on this board before and still support this viewpoint as it is the accepted national standard, but would be fine keeping Mom and babies until 12-13 weeks. But to hold kittens until 4 months is crazy to me. They go past their cute kitten stage (which is when people want to adopt) and become too bonded to their foster home- I fear they will have a really hard time adjusting when they leave my care and then are separated from each other. The rationale behind the change is that several kittens died of FIP last year and the thought process is if they would have had later surgeries they would have survived. However, there is no logical connection between FIP and surgery- my non-medical understanding is that vet's are unsure what causes FIP but that it is 100% fatal in all cases. If a kitten has it they will die regardless all other circumstances. There is also a host of other problems that will come from holding kittens in shelters for this long: those that have been caged from birth are going to have an incredibly difficult time becoming socialized, not to mention kittens can reach sexual maturity as young as 4 months, meaning they are risking litter mates mating with each other. 

I pushed to keep Mom with me after her surgery but it is "against shelter policy" for a healthy, adoptable cat to stay in a foster home past the weaning period. I hate using the term "property" when referring to animals but it's the best description I can give- in these situations the cats are the "property" of the shelter, and there is little I can do as a foster to go against their decree. I'm heading in today to try and get Mom back, but if they still say no, then my only options are: a) send the kittens back to live in a cage until they reach 4 pounds which I morally cannot do, or b) keep them sans Mom and do the best that I can. 

Their not telling me about the policy change was the icing on the cake of many problems so I have resigned pending the return of these two fosters. The shelter's mission is to serve the best interest of it's animals, and separating a Mom from her babies unnecessarily and holding healthy kittens past their developmental prime does not serve that purpose. I will still foster, it will just be for another shelter. 

Sorry for the rant- I'm very frustrated right now over the politics of this situation and it needed to come out. Thanks ClaraAdele, I have some bitter apple so I will try that if I fail on my mission today. Any other suggestions are greatly appreciated!