It can vary by area, but I think your rent estimates are low. We have paid as much as 800 for a 1 bedroom flat when we lived in an expensive area. After moving to a smaller town, we paid 800 for a 3 bedroom house but have recently moved again and are now paying 1050 for a 3 bedroom house. I think you'll want to budget for 800 at least (if you're willing to have your kids share a room, you'd have more luck finding a 2 bedroom for 600).
I'd also look again at the tax calculators online--I would think your take home wage would be around 1900 (less if you contribute to a pension).
Childcare can be really expensive here, as well. For full-time, 5 days a week care, the minimum amount we were quoted was 1,000 a month (with some places wanting up to 1300 a month). In-home childmilders will be more reasonable than nurseries.
For what it's worth, my husband and I have been living on his post-doc salary with one child for the past 2 years, but in order to make the costs work, I had to quit my job and stay home full-time. Definitely doable, but we are moving back to the US after our second is born, as it's not something we want to do long-term.
