Your are assuming at least two things (there are surely more) about people who are struggling to raise kids

1) They have always been struggling, a didn't have a reasonable plan originally, and/or

2) They didn't take reasonable precautions to avoid pregnancy but still end up pregnant, and believe their best option was to raise the child

Both of these assumptions are clearly false in general although I don't know enough about the issues to hesitate a guess on percentages.

I was mostly thinking about (1). Someone with a partner and a solid household income can easily become a struggling single parent, for example, without having made any obviously bad decisions.