As cold as it sounds, IMO, the charges seem appropriate. He drove around a barricade into a flooded wash and no matter how good or honorable his intentions were, those actions resulted in the loss of 3 children.
The whole situation is horrific and this seems to be one of those cases where there is absolutely ZERO upside to any legal action and prison time will not benefit the the families, himself or society.
Unfortunately, no upside to a prosecution doesn't mean you automatically get a pass.