I'm glad that you're being thoughtful about kids - whether you want them and what impact they will have on your life goals and finances. Certainly you can raise kids in more or less space, and with more or less "accountrements," but it is unavoidable that they will have a huge impact on your life and your lifestyle.
What I can't tell from your post is whether - separate from the financial impact - raising kids is appealing to you? For some people, it's a central storyline for meaning in life, and they can think of nothing better in terms of how to spend their retirement than with their adult kids and grandchildren. For others, it feels like a burden and a distraction from what's most important to them - whether that's career, FI, hobbies, travel, doing their part to improve society, etc. It does sound like your partner is more in the first camp, and you may be in the second.
That's really tough, and the decision is complicated by the fact that I do think it's hard to fully understand and weigh the emotional side of having children until you have them - both for worse (stress, self-doubt, anger, boredom) and for better (joy, pride, amusement, friendship). I have always thought of myself as a pretty even-keeled midwesterner. Becoming a mom broadened the bandwidth of my emotional reactions by about 3x in each direction - I can instantly become more furious that I'd ever known, and burst into tears of joy faster than I'd ever done. And simply by seeing one of my kids be either unexpectedly mean or unprompted-ly kind to their sibling.
Plus, everyone has different years that they find most challenging or most fun with their kids. The infant/early toddler years are super high-maintenance and low sleep. I found the 12-20 month window the toughest with each of my kids - all they want to do is move, and they have no sense of danger or interest in sitting still to give you a break. Now that my three are 16, 13 and 9 I feel like we've been living quite a while in "golden years" where they are funny, fascinating, increasingly capable, wonderful travel companions, and teach me something new almost every day.
My husband has 3 brothers. All four of them knew they wanted kids. One of the wives has not been able to get pregnant, and is now 44, so they are really mourning that loss (and still thinking about adoption). The other two wives were quite unsure they wanted kids at all. One because she didn't feel she'd be a great mother, and she knew her husband would not be willing to make the sacrifices in their careers that were needed to raise kids (they both had very high powered 24/7 travel-all-week jobs) even though HE'S the one who wanted kids. The other because she loves her career and she didn't want to scale back herself. In both cases, the discussion/conflict about whether to have kids went on for more than 5 years. And in both cases they decided to have them.
In the first case, the wife was initially right - dad still was away all week in London, etc. But nonetheless she said he was right and it was the best decision she made. She died of breast cancer when the girls were 3 and 7, and dad quit and has been home full time with them since (they are doing well, and live down the road from us). In the second case, the wife absolutely adores and dotes on her firstborn (she is pregnant with #2 now), but I think she finds motherhood more stressful than she expected it to be, at least at this stage. So it's a bit more mixed for her.
All this is to say that there isn't a right answer, but talking about what is appealing or scary or worrying for each of you will help. And thinking about what meaning FI, kids, life, retirement has for each of you. What's the ideal for how you'll spend your FI time when it does arrive? How does parenting - or not - fit into that picture for each of you?
Good luck!