1800 miles in 3 days with 3 kids in a truck. Crazy or not

As you already know. 600 miles will be 12+ hours per day. You will NOT average 60 MPH. You will be lucky to average 50 MPH by the time you stop for fuel, stop to eat, and stop to use the restroom.
And all that depends on nothing going wrong.

Remember professional drivers are limited to 10 on duty hours per day, and they don't have the wife, and kids in their ear. I'd think about it hard.