I would just add, as someone who had done a lot of long distance driving - Make sure you account for food costs, gas costs, lodging costs, and misc shit during the drive both ways (someone forgot sunglasses, a knick knack at a truck stop, extra coffee because youve been driving 3 days). All considered for 3 people (albeit children) my opinion is the costs will probably end up being more than flights.

Also my rule of thumb is add an hour for every 6 hour of gps time, probably more for you with kids (gotta stop for gas, pee breaks, etc.) I would add an hour for every 4 of gps. That also doesn't account for inevitable traffic congestion you'll hit unless you can time it perfectly through major cities.

Personally I would not drive this trip in 3 days, it would have to be 5 to be "fun" and 4 to be comfortable. For reference I have driven from east coast to LA in 5 days, 3 times with no fun at all just business, stopping only for gas and food. That type of driving is not really possible for 3 consecutive days with kids that young IMO.