Hi B. -
I stongly encourage you to allow them to be a part of this process. As parents, it is natural to want to shield and protect our children from all the hurt of the world. Loss is something that they will face and you want to allow them to deal with it in a healthy way. Also, your uncle's children are going to need a lot of support and love and I assume your children will be a big part of that. Also, allow them the opportunity to spend time with your uncle (and him the chance to enjoy them) while he is still here.
I am sure your kids have heard you say that he is "sick". Please be careful to also make sure to use the word "cancer". When we tell children that someone dies because they are "sick", we leave it open for their very creative minds to interpret. The next time they get a cold or a friend is home "sick" from school, they become fearful that they might die too. Be honest and be clear. They will have a lot of questions. Some will be innocent and beautiful, some will be hard to answer because you are grieving too and some questions simply do not have answers. Remember you must be fair and allow them to work through this process as well.
This past January our youngest son passed away leaving behind four older siblings (ages 2, 3 1/2, 5 1/2 and 9). It was a devastating time for all of us and thankfully we had a lot of help and guidence along the way. We allowed them to set their own limits and did not force anything upon them, but they did participate in every step of the process. Like some of the other comments mentioned, sometimes they don't seem to get it (like "OK, can I go play now....") and that's OK.
We had some private time with just us and the children prior to the visitation. We allowed them to approach his casket when they were ready and ask questions freely. One of our children had made a card to leave with his brother. We also arranged for the kids to leave the visitation early and have a slumber party and relax with a close friend of the family. They were able to be a part of it and spend some time with their brother, but it also allowed the adults the time to visit and grieve as well.
During the funeral all of the kids presented a gift to leave with him. Throughout the celebration their expressions and grief would come in waves. It was painful to know that they were hurting, but they needed the opportunity to say goodbye just as we did.
For a couple of days our 5 1/2 year old would tell everyone (server at a restaurant, cashier at grocery check-out, etc.) very matter-of-factly "Did you know my brother died? Yeah, he died." Thankfully it went away quickly, but it was just part of how he was processing. Our 9-year-old doesn't really bring it up. Every once in a while she'll participate in a conversation with the other kids about what Heaven might be like or whether or not Rocco has wings now, but mostly she keeps it to herself. The younger kids were more upset that we were sad or crying. They still talk very openly when they miss their brother and want to look at pictures and talk about him. We allow them to talk freely and express their feelings. Thus far they have been very positive and very kind and often look to see if he is dancing on a cloud.
We did do some counseling - as parents, all together as a family and individually with the kids. It was a good tool, but they really are doing just fine. Kids are so resillient and the innocense is beautiful.
There are a lot of resources available - please take advantage and continue to reach out to others who may have had similar experiences. It is comfoting to know that you are never alone. Please feel free to contact me at anytime. My email is ____@____.com
I am very sorry for your family and the challenges you are facing. I wish you much continued health and healing.