It must be hard if you aren't enjoying what you need to do.... but it may help to think about the following:
You say your dd loves nursery. Focus on that. She is fine. You may not be having exactly the lifestyle you want, but the important thing is that your children are not suffering - which they would be if you lost your home or were suffering the terrible stress of not being able to pay the bills
In the long term, you may be very thankful for staying in a good job, where you have security, prospects etc. I see so many women who are desperate to even get back into minimum wage work after taking a few years out, and struggling to achieve it. So what seems awful now, could turn out to be a blessing in disguise, when your children are both in school all day. I suspect you may also rediscover your love of your job then, as you say its fulfilling and something lots of people would like to do.
Have you thought about varying your routine at lunchtime, if it upsets you seeing mums and babies about? Could you work through your lunchbreak and leave earlier? I am a teacher, and one thing that I found helped a lot when I returned to work when dd was 12 weeks, was that I was so busy literally all day, that I honestly didn't have time to think about her. I always worked through lunchtime which I think helped. Sometimes I would get to the end of the day and think 'Ooh I've got a lovely baby to pick up from her childminder!' Maybe sounds odd, but if you're really focused on work, then you really do learn to compartmentalise.
Finally, how about considering you and your DH both cutting back a bit, so you each work a bit less than full time, which will give you more time at home, without dropping your income too much, or harming your prospects?
There's a lot of variation between working full time and not working at all, and it may be that some readjusting can provide you all with a lifestyle you're happy with