Death is incredibly hard for everyone. It's possible that your husband doesn't want the last memory he has of his mother to be the one where she's hooked up to life support. There are a lot of people that simply can't handle it. It's not that he's wrong or right, it's just the way he chooses to deal with it.
Personally, I would want to be there to say one last goodbye, but that's me. If you want to go, I say go. Say your goodbyes to her. I wouldn't take the kids. It might be a natural part of life, but your kids are so young, they wouldn't really understand what's going on.
I'm sorry to hear about your MIL. It's never easy to lose someone.