We stop every hour to 2 hours. When we need gas, when we eat etc. At those stops we take our time and let the kids rest for 10-15 min. Half way we offer water although they rarely take it. We keep a hay bag in front of them all the way too.
If your hauling with a truck, you're going to have to stop for gas every hour or so anyway. Just take a bit longer than you would if you were by yourself and making a quick stop.
"Until one has loved an animal, part of one's soul remains unawakened..."
- Anatole France