I had four cats who I loved dearly and thought the world of. I was cat mad, thought they were greatest creatures ever. When I became pregnant, I started going off them, it was like something had really changed. Then I got DS's cot all made up and ready for his arrival, only to find one of the cats had jumped in a few minutes later. I went mental. I did feel a bit guilty but put it down to hormones.
Then when I had ds, I went off the cats even more, I used to love having them on my lap but just couldn't stand them coming on to my lap or needing my attention. I did feel bad that I had treated these cats like my surrogate children and then when i had a real baby, it's like I didn't need them anymore!

I was a single parent from the start, and when ds was a few months old just felt I couldn't cope with the cats anymore, and gave them to the ex p I was with when we originally bought the cats. He was disgusted at how I could just palm them off so easily when they had meant so much to me before, but I had different priorities.
Fast forward 6 years later, I've just bought a kitten. I'm well over the resentful feeling I had with cats, and I adore our new kitten. But still, I bought the kitten for ds and I love this kitten for providing so much pleasure for ds, so it's a slightly different attachment.
So yes, things do change when you have children because your priorities do, and should, change.