Depends on what time of year you are doing it, if during the winter months I would drive, because it could be a bit chilly taking the boat at night.
Plus your probably talking 90 minutes min by bus/boat and 20-30 min if you drive. 10 min to get to the Outpost bus stop and another 10-20 min waiting for an internal bus to take you to Pioneer Hall. You can't drive right to Pioneer Hall.
Keep in mind that the MK has to be open for you to take the bus there.
IMHO it's a no brainer especially with the little one, use the car.
If using bus/boat I would leave 5:15 at the latest, if by car 6:30