Depending on what time you'd arrive you may find that you waste a fair amount of time checking out and in again on the Sunday as you have to check out by 11 and can't check in again until 3. I can see advantages and disadvantages to the idea it does depend on how organised you are.
I think you will get a decent feel for HH in 6 days and if you want to go looking for activities you'll have no trouble finding them, but with kids of 8 and 11 I think they'll have a great time around the pool and beach.
We've driven from Pitts and it took about 12 hours. In your position I'd leave Saturday morning (not too early) and drive until about 6-7 in the evening. Find a motel just off the Interstate, have something to eat and a fairly early night. Get up reasonably early and complete the drive (probably a couple of hours) and arrive at HH just before lunch. Let the kids have a couple of hours in the the pool then have lunch just before you check in (forces the kids to have a little break after lunch). If your leaving HH on the Friday afternoon/evening I'd drive until maybe 8 and stop again at an interstate motel , finishing the journey Saturday, leaving you Sunday to recover. IMHO driving in one shot REALLY takes it out of the driver and by keeping to "drive 4/5 hours, break for a meal, drive 4 hours break for the night drive 3/4 hours" it means the driver arrives at both ends of the journey in a suitable condition to enjoy themselves or go back to work. I wouldn't bother booking a hotel because although it may save you $20-30 it ties you to a "target" stop. By just winging it , it allows you to decide when you need to stop and it gives you the flexibility to deal with any emergencies that may arise.