It is up to you to feel out the situation with your kids... but here's my opinion...
Your kids are too young to few the body or wait through a long ceremony.
However, I was just at a funeral/viewing in March and at most homes, there's a large lobby area and a refreshment room outside of the viewing area and the funeral service. There were lots of younger cousins and toddlers running around the halls and in the refreshment rooms. Relatives took turns spending time with the young ones... a pleansant relief for the relatives... while the adults went to the viewing and spent time with the bereaved.
At the actual service, there is bound to be teen cousins around that don't want to sit through the service, but hang out in the lobby with the younger ones.
I think it's good to have them there and explain where you're going, why you're sad, etc etc but don't make them sit through it.
If you don't have a large family with younger cousins then leave the kids at home with a sitter or trade off with your husband.