Pre- or post-nuptial agreements are no doubt one of the best things you can do to protect yourself, but it will only go so far as already mentioned. If you accumulate a lot of wealth during the marriage, it's likely going to be split and set back FIRE plans. There is no doubt that divorce is a gigantic threat to FIRE, and the 40-50% likelihood is a monster. Oh, young, naive people that think because they're on the same page now, it will be that way in 10, 20, 30 years!!
Child support laws are about the most Anti-mustachian thing you could ever dream up. They typically allow support amounts to go to stratospheric levels, based solely on income, completely confounding any idea of frugality. And they are paid to the ex-spouse to use as s/he sees fit, not directly to the children. That is, the support is often used to subsidize the ex-spouse's lifestyle, not the kids.
As a simple example, if 20% of pay is taken for "child support", then on an income of $100,000, $20,000 would be paid in child support. If the income is $1 million, then the support amount would be $200,000. What child needs $200,000 to live on? Forget arguing to the court that the amount is excessive and would just encourage your kids to be spoiled brats or supporting your ex's lavish lifestyle -- the court will go strictly by the numbers. Michael Strahan of the NY Giants infamously had to pay his ex-wife over $1 million/year in "child support", even though she already got tens of millions of dollars in assets in the divorce settlement.
And, forget RE as far as child or spousal support are concerned. You will be assessed the same amount of support whether or not you retire early. As far as the laws and courts are concerned, your income will be assessed at whatever level you are earning until you are 65 at a minimum. If you retire early, and your income drops, the courts will ignore it since it is considered "voluntary underemployment." Meaning, you are locked into that earning level for the rest of your life, you can't voluntarily reduce it and have the support amount reduced with it. Even people (almost exclusively men) who have taken "early out" incentives only a few years before reaching age 65 because they were about to get laid off still have not been able to get support amounts reduced.