Oops, I meant the Middle Fork not the North Fork (see below for previous message rafting with kids)

Because you give us little information about your, your husband's, or your kids' experience level, it is unlikely that we can give you a meaningful discourse/advice on this matter.

let's Put it this way: if your husband is a long time silverback riverguide, and the family boats pretty frequently, this could be a great trip.
If your husband is an occasional boater and the family boats infrequently, this could be a great trip or a harowing trip, depending....
If your husband is relatively inexperienced, and the family is brend new to boating, you could become a river statistic.

Just depends on your collective abilities.

Oh...also, you didn't tell us which run your hubby was talking about. If it's the class 2 run, then move your group's risk profile in the above list so that less experience = more fun, less danger.
I was assuming you were heading down the tunnel chute run, which is the one most experienced boaters would think of when "running the middle fork" is brought up.
So, which run are you actually planning on?