My guess is that many of them will use their free time to make another couple of kids and raise their income with another 1000.
If the question would have been 'what would you do', I think I would have quit my factory job as well, actually.
What you suspect of other people tells a lot about you, and very little about other people. I would be careful with that.
But besides those sources there is also the fact that the child-raising benefits are only unconditional from the second child on, for the first child there is a maximum monthly income to get it.[2] If the main goal was the well being part, then this would not make much sense.
[0] http://www.thenews.pl/1/9/Artykul/250612,Poland-pays-out-mil...
[1] http://nytlive.nytimes.com/womenintheworld/2016/02/11/poland...
[2] http://ec.europa.eu/social/BlobServlet?docId=16077&langId=en [PDF]