If I had to drive 4.5 hrs I would plan on stopping at least once if not twice for a break. It really depends on what your limits and sx are.

For me, my driving is limited by neck pain and fatigue, and the neck really limits where and how I drive. It limits all my travel really, even if I'm not in the driver's seat.

The thing that concerns me is, are you sure you're up to this? I know you hate to dissappoint your child. But you may want to consider how the stress of driving, the worry about being so far from home, all the activity, etc will affect you. Kids get over dissappointment and can deal with Plan B, when they need to.

Changing your plans is an option, if overcoming the sx is not, okay?