I had children without being married.
My partner wanted to get married and I didn't. I thought perhaps I could get over my emotional issues with marriage in the future but I couldn't leave having children indefinitely.
I did not get over my emotional issues with marriage as essentially I didn't really trust him (and didn't want to admit this to myself). I was right not to, and he left me.
I wouldn't have had children at all if I had waited for marriage. And I am very glad I do.
Materially things worked out well for me, as I was always the harder worker and I walked away from the relationship with more than I would have if we had been married, as certain assets were in my name (because I had paid for them).
Having small children was tough on the relationship and probably contributed to its end in some ways. However, although it took its toll on us, it would have been harder in the early years if he had left sooner. Although he was a git about it, he didn't do literally nothing, and I don't know how I would have kept all the balls in the air - work, babies, etc - if I had been on my own.
I wouldn't, if you are planning to take longer than maternity leave off work.
If you're going to work anyway, that's different. But discuss what having kids will mean to both of your lives. Some men think (subconsciously - most would never admit it) that they are owed a life untroubled by domestic or childcare duties. If you have children, and if their mother also WOH, they can't get away with that, and they may resent the woman. Having small children is hard work and many men see this as unfair work inflicted on them by their woman (even if she is working much harder and contributing materially too). Find out if your man has these attitudes (he won't admit it but try to find out anyway).
If he does, you have the choice:
ltb (hopefully to have children with someone else?);
have children anyway, knowing that you will continue to WOH, that rocky times are ahead, and you may end up alone (but you are guarding your independence and this is something you can deal with) (outside chance that having children will educate him and he'll turn into a better man);
accept that if you have children with this man you will be stepping back from work, taking on a very domestic and child centred role, and in that case GET MARRIED.