Rsdr, what cruiseline are you sailing on.? Where on the ship will you feed the kids early, will it it room service, or a buffet?. If your're dining goes on past 10 many kids programs end at 10 and it is paid group sitting,also check that the program runs through the dinner hours.
On Princess they have Anytime dining, and we had it and loved it, we would have thought that would be the route to go with kids so that you can choose when to eat and not be under a time schedule.
I don't think Carnival or Rci has it.
BtW what about going to shows, would you go before dinner or after, will there be sitting that late, and do you want to wake up a 5 yr old and carry her back to the cabin that late? Remember that if the next day is a port day, then you all have to be up early, unless you don't plan on doing anything.
I guess my view is that the early seating would have been better, you could still feed the kids early, send them to the kids programs, have dinner and time for a show or a drink and still have everyone back in the cabin at a reasonable hour, or course I realize many people don't mind their kids staying up late , and your oldest two kids are well , older, but I know most five year olds can be a bit cranky if kept up past 10 or 11.