Hello OP,
Firstly, congratulations on your pregnancy and the offer of a new role
From my own experience, knowing what I know now, I think I wouldn't take on a more senior role in a new company.
I've been back at work about 8 months now, 4 days a week (DD2 is 19 months). Honestly, it's taken me the best part of 6 months to feel that I'm mentally as sharp as I was pre-pregnancy (that said, in the past month or so I've been pre-occupied with sorting out childcare for my eldest for when she starts reception).
When I came back to work, my role was pretty much the same as before which gave me time to re-adjust back to working life. However, in the past two months it's morphed into me taking on much more responsibility, being involved in projects that are meant to result in a huge cultural change within teams and therefore having much more visibility throughout different departments. I can tell you that it's been a struggle at times - and my job doesn't involve travel, I do a strict 9-5 with a 25 min commute, my husband helps out AND I have a hugely understanding boss who will not bat an eyelid when I say I have to WFH certain days because my kids are not well. Oh, and for the first 5 months of being back at work, I was battling severe sleep deprivation as well as DD2 was teething badly and would be up every 1.5-2 hours throughout the night (and of course, only mummy will do!).
What's the work/life balance like in the new company? Should you feel like it later, would they feel happy with you doing flexi-work? What support will you have with childcare? If both you and your husband are working long hours then presumably you'll need a nanny ... and presumably you may not be there to put the kids to sleep every night. Are you OK with that?
Someone said: "I don't mean to bang the feminist drum but we have a situation where you've been offered a great job and you sound like you want the money/new role. But because of all the perceived baggage around working mums you are dealing with an extra layer of stress." I agree with this, but my reality is that when my kids are not well they really only want me, no matter how much they love daddy. Which means rightly or wrongly I'm the one with the added stress, and the one who has to be around when the kids need me, job or no job. So for me at least, being in a role that allows me to also be around when my kids need me is far more important than any career progression.
Lastly, I would not presume to tell you what to do, just that it DOES take time to get back into working life after mat leave, and you shouldn't underestimate the challenges of going back to work with two little ones. And that's to a familiar role, in a familiar environment.