Kittens "suckling" each other.

Hi guys,
I have seen other posts similar to this but the situations are different so thought I'd see if anyone can offer advice on mine.
I am fostering 4 kittens, between 5-6 weeks old. Mother cat was taken home a few days ago (I know it was too soon).
Last night I noticed the kittens suckling each other (not genital area like in other posts), and pushing the stomach area of each other like they did with mum cat when feeding. They have been wormed recently. Have food (wet and dry) available almost 24-7 to help themselves to.
Is there anything I can do? Or is it perhaps a comfort thing?
Any advice would be appreciated. Thanks

Should not be anything worrying, unless it goes to excess.

It may in some degree be a comfort thing as you say.

The only real question is, if it is mostly for comfort, how big is the need of comfort? Is there something you can do to give them more comfort?

That is the question.

The suckling as such is not dangerous and quite common.

Good luck!

Very common in cats taken from their mother too soon, they are doing it for comfort and because they should still be nursing.

Just watch that they don't cause sores on each other from the suckling. 

I had five boys that suckled on each other and it was a big problem. They were literally sucking on each others parts constantly. It got so bad, I had to separate them when not being supervised. Not only where they irritating each others penis' but they were ingesting too much urine and were failing to thrive.

One actually went on to needing to wear a collar for a few days as he began drinking his own urine instead to water.

This obviously is one extreme but be diligent. I waited too long to separate, fearing they would socially suffer.
 

Suckling is usually both: being pulled from Mom too early and needing some comfort and reassurance. 

A lot of the time it's not the big of a deal but, like Levi68 mentioned it can quickly spiral out of control. 

I always try to nip the suckling as soon as I notice it. Once they get into the habit it becomes extremely hard to break and can have other unintended consequences. I.e. trying to stop them once they are used to it can lead to other behavioral issues.

The best success I have had is with bitter apple. I get the kind that can be rubbed on and that doesn't have any alcohol in it. I rub it on each of the kittens stomachs. Since they dislike the taste they will usually stop doing it so long as you are consistent in applying it. 

The thing to watch out for using this method is that they may start suckling elsewhere. It could lead to genital suckling, suckling blankets, or even suckling you. Like Stefan mentioned at that point you just have to outweigh the benefits with the risks. Since they are fosters a big part of your concern is making sure they are "adoptable." Most adopters will overlook a kitten that suckles a blanket but one that suckles other cats or humans is likely going to be a problem. 

So, I would start by using the bitter apple. If that doesn't work you may have to separate them unless supervised. 

Good luck!