At the very least, this could be creating an emotional dependence and have a negative affect on their ability to become independent. On a worse scenario, there could be something very unhealthy going on. In most states a parent sleeping with a child of the opposite at the ages you mention is more than frowned upon and may in fact be cause for intervention by Child Protective Services.
You may be hesitant to report this, but erring on the side of caution is worse than taking no action.
There are some things in life that are just simply strange. I agree with the jumping to conclusions that something, "unhealthy" may be going on although its not always the case and its important not to jump to that conclusion because it could cause major damage. Some parents really do love their children enough to want to spend all their time with their children and of course these days with working so much nighttime seems to be the only time we can actually spend time with them and it seems to make someone feel less guilty about not spending enough time with them.
I do beleive something needs to be done, but I probably wouldn't go to such drastic measures as to call DCFS until you KNOW without a doubt abuse is really going on. They are difficult and scary to deal with and it may be more innocent than it seems. We naturally as humans want to assume the worst, but in reality it may not be that bad. Yes it is enabling the children to be very co-dependent and will more than likely result in serious problems as adults in all aspects of their life. I am assuming you have already mentioned this concern of yours to them. But try this approach next time, do some research about co-dependence, sleeping with your children and how much harm it will do to them for the rest of their life. It will surely be a one way ticket to an abusive relationship. Print out material to bring to them and don't be on the definsive side, they are probably like most of us good parents and want our children to know we love them, although they are going a bit overboard. Try as hard as you can to empathize with them and have an open mind because we all parent differently and sometimes we need help not only from professionals but from our family. Eventually if you can get through to them I would try to suggest counseling and reassure them they can still deeply love their children even if they are in the next room in their own beds.
I AM 28 YEARS OLD HAVE 1 CHILD THAT IS 7.I STILL SLEEP WITH HIM.MY HUSBAND WORKS NIGHTS AND I AM A STAY AT HOME MOM.I LOVE TO CUDDLE WITH HIM AT NITE. I FIND NOTHING WRONG WITH IT.AND HE DOES NOT HAVE ANYTHING EMOTIONAL GOING ON NOR IS HE DEPENDENT ON ME THROUGH OUT THE DAY HE DOES HIS OWN THING LIKE ANY OTHER 7YEAR OLD JUST AT NITE HE WANTS TO FALL ASLEEP WITH ME.THE WORLD HAS COME TO THEY DO NOT HAVE TIME FOR THERE CHILDREN AND EVERYONE WANTS THEM TO GROW UP TO FAST AND BE SO INDEPENDENT.