V.B.
I think you should allow the children to decide individually. I would not ask them as a group... but one at a time, talk with them privately and ask if they want to be there or not, and if they have any questions about it or about how they are feeling.
Some may want to be there, some may not. There may be guilt with either choice, and that is what you want to help them with... if YOU and husband make the decision, it removes the guilt from them, but they may be angry with you later, if it wasn't what they ultimately wanted.
The 4 year old is the one that would be hardest though... that isn't really old enough to understand much, no matter whether they stay or don't. But if the older kids stay, I'd lean towards letting the 4 year old stay also...