We're not really saving anything specifically for his education for a couple of reasons:
1) Nobody did for us, and I never went to university - started my own business instead and am doing just fine. Wife went to school and her family spent tens of thousands for her to get a degree in arts that isn't used at all (not for lack of trying..it's just really hard to make money at it). Instead she also runs her own completely non-related business that had nothing to do with her education.
2) We've got junior that German / EU passport meaning he can go to university there, free of charge.
So let me (softly) encourage you to re-think this, just a little. First, you're a smart guy, you know that your and your wife's situation is not necessarily representative of everyone's. There are a lot of jobs that do require degrees. And even worse, a big -- and growing -- issue nowadays is that many jobs are using a degree as screening criteria, even if the job doesn't need it. For me, I want to be able to set up my kids to pursue whatever (reasonable) path they want. Maybe your kid would struggle as an entrepreneur but would make an awesome engineer. But if you've planned on the first path, it's harder to change to the second; OTOH, if you plan for the second and he follows the first, then the only downside is you saved more money you now don't have to spend.
Second, IME, even the trades and similar routes are now pushing toward some type of post-HS education (my HS used to offer a vo-tech course that allowed kids to attend school half-time and learn a trade the other half of the day; now it's the community college that offers things like welding and plumbing courses; my brother just went to culinary school and it cost him like $50K, I shit you not -- all to work in a bakery for $9-10/hr.).
Third, if you want to be an entrepreneur or run your own business, it's good to be able to afford some accounting and business classes -- I've watched way too many businesses go under for lack of a clue (e.g., the store that opened and closed within 3 mos -- wtf? How can you open a business and not have sufficient cash reserves to cover your bills for 3 mos.??).
Fourth: honestly, if you don't save anything, and your kid wants to go to college in the states, he is fucked -- college costs are soaring, and people truly have no clue how much the expected parental contribution turns out to be. It is getting harder and harder to work your way through school -- or, at least, to do so without taking a lot of extra time to graduate, or taking on a lot of loans (either one of which will set him back on his journey to FI).
And fifth: no one knows what the future holds, and having a little extra cash set aside never hurts. Maybe Germany will change its university policy by then, or maybe your kid won't qualify. Or maybe your kid doesn't go to college but you want to help him with a downpayment on a home. Etc.
In sum, you framed this post up as maximizing opportunities for the kids. One way that many parents do that is to make sure their kids can afford go to college, IF they want to and can get in. Because for those kids for whom college is the right choice, being able to graduate in four years, without a lot of debt, is a huge leg up towards their own financial independence. It also doesn't have to mean committing funds specifically for that; we have a VTSAX account that is mentally earmarked to cover college stuff, but if we don't need it, hey, it's in our names, more money for us!
Obviously, you don't have to save anything if you don't want. You can decide that your kid will learn more by paying his own way and being independent earlier, or that college is overrated, or that your kid can take over your business, or whatever. Just suggesting some things to consider given the stated goal of maximizing opportunities.