ADDED after your SWH:
At 9 and 11 your kids are old enough for you to say frankly, "Cousin Age 13 may try to play around. This is not the place. You will stay with me while we are there, period." Sounds like your real issue here is the one 13-year-old cousin's possible behavior. I might ask his parents what time they probably will be there -- then avoid that time if you can, without telling the parents that. But you can't avoid him or her forever, so setting strong expectations with your own kids is key. You cannot control this other cousin, and don't try to; that is his parents' responsibility and if he is a jerk at the "calling hours" -- well, you have no control over him, but you do have it over your own kids.
Original answer:
Yep, as previous poster said -- very difficult to help you if we don't know your own kids' ages.
By "calling hours" do you mean what I'd call a "visitation" where the body is in a casket at a funeral home and there are specific hours when people can come to the funeral home, and stand around and visit briefly with the family to express condolences?
If that's what you mean, the answer's pretty easy. No "calling hours" visit should be long enough that the cousins have any opportunity to start "acting as a pack" and playing around with each other at all.
You and your husband can both go. Drive separately so one of you hauls the kids away after a short visit. Whichever one of you was closest to the deceased is the one who will do most of the visiting, while the other one of you is in charge of your kids -- YOUR kids, not all the cousins too. Tell your own kids in advance, before you get there, that this is not a time of place to talk and play with the cousins, especially if your kids are used to playing with these cousins.
Take your kids up to say words of sympathy or share a memory with the deceased person's very closest relatives (rehearse this beforehand, so the kids don't suddenly go all shy or try to get away; if they are very young don't do it at all). Then you take the kids off to the side to let the other spouse, the one who was closer to the deceased, visit without the distraction of kids.
Then you leave! Your kids will get restless and bored if you stay and stay. Be quick. The spouse who is the main visitor can stay. Everyone WILL understand when those with younger kids make short visits and leave, especially if the spouse who was the main connection to the deceased person stays behind to visit.
If you kids are older, set expectations with them and be very clear that this is not a social time for the kids. And even older kids shouldn't stay very long. Older kids should indeed speak to the closest family members - it is the right thing to do and the polite thing.
It sounds as if you and/or your husband expect this to be a lengthy affair where you and your kids are expected to stay and stay and therefore you are worried the cousins will all start playing around, but in our area at least, these events are just not like that. If this is instead a "wake" at a relative's home with food served etc. then you will have to basically keep your kids close to you, bring something individual and quiet for them like books, and again -- leave early.