IMO... Dawn dish washing detergent, a pressure washer and keeping away from key parts...
You do not need the Dawn, it is a cheap cleaner though. A pressure washer can be too abusive, expecially on radiator fins...
You want to keep the water out of 3 key areas, the oil, the diesel, and any exposed electronics. Supposedly a tractor is "water tight" in terms of electronics, but with a pressure washer things will get under the skin quick.
I generally do not wash around the fuel tank caps, nor the oil tank caps. On the engine make sure your caps are on tight and don't spray them directly...
Some people don't clean alternators (I disagree with this) and starters - Both should be engineered to take the water...
Anyway.. . The most important tool is your kids, make them go do it and sit and supervise...