I speak for the countries where I have experience working. Most frequent scenario for me was: In the beginning they mostly earn +- the same amount (grosso modo), although women are much more likely to already work part-time (statistics). Or more in a caring profession, e.g.: a Latin teacher in a secondary school (very noble and interesting profession but it pays peanuts). On top of that, as the relationship progresses the woman works more part-time thus damaging her earning potential (again statistics). Mind you I could/can also see it in action in real time. At the beginning there were more women (more female graduates), suddenly they disappear to not to be seen again (side-tracked, different less taxing employment, who knows). Mostly around the time they want children. Off course there are women who do things differently, but I’m talking about the scenario here.
If you’re going to do something like that scenario, it would make sense to marry before you have children. Afterwards you’ve made it more difficult for yourself, less appealing. It would be quite an unnecessary risk for the partner to marry afterwards. I suppose you could also do everything to insure that both partners take on an equal share of everything (and probably work less/outsource more – not everyone’s cup of tea). In reality this is probably an illusion; it’s almost never equal and most of the time it’s the woman that gets the short end of the stick from a financial pov. If you can get the things you desire without marrying, you have quite an advantageous arrangement. Someone is enabling your career/children whatever, it’s quite cheap, and if you decide to bugger off it has relatively little consequences. Sure you can own assets jointly, tontines and all that; but not a lot of people do something like that. If you want, you can work something out that will provide similar protection as marriage, but again not a lot of people do that.
Prenups, marriage contracts, division of property … all valid over here. You can do whatever you want. Still the easiest way out is saying that you’ll most definitely marry the other partner, you just don’t know when. Mostly you’re not going to find a lot of (wo)men that are willing to sign a marriage contract or something similar concerning something major. Most want the default system. Save yourself the argument, dangle a carrot. From a moral point of view this is quite dubious.
I don’t see how, in the scenario above, you can get paid for your unpaid work that undoubtedly helped the other partner without a marriage/or a construction that closely resembles that, when the relationship ends. Divorces can be quite cheap. Money isn’t everything, but it sure helps. If you’re the financially stronger party, most of this probably doesn’t apply.
Children don’t really mean much in terms of commitment, they just make your own situation more difficult.
Do whatever you want, but know what you’re doing.