I'm okay now that the kids are all at school, but I used to write at night or whenever they went to nursery, it's difficult - I used to feel so selfish, ought to be doing stuff with the kids, or the ironing/washing instead of being so self-indulgent...still do, there's always things to do, and if like me, you are unpublished it is hard to for anyone (me included) to take writing seriously, the little hobby!!
The kids won't be kids forever. I'd say enjoy your wee baby, you'll get a routine in time, no point getting in a tangle about it - they come first, second and third...sleep is fourth...as I'm sure you have discovered already.
One thing I used to do, was write longhand, say jot down character backstory or the elements I wanted to include in a scene while they were eating lunch or in the bath, things I could do quickly that didn't require a huge amount of concentration. I'd only go to computer to write when I had a good stretch of time to commit. Good luck.