Yeah, yeah... I know that kind of story.
This isn't the complete picture. You are presenting anecdotal evidence, and omitting important details. Some important details you are ommiting:
1A) For the job you provide, is the QoL of the work low compared to the wage and potential health hazard(s)? This seems to be the easiest counterpoint to your entire argument. You also lack statistical relevance. 1B) You omit the question wether those workers were easily replaced. If yes, what type of income & benefits did those people receive? If no, why not?
Aside from that one:
2) Which other social benefits exist in Poland?
3) Are these affected by child support benefits?
4) How exactly do the various tax systems work in Poland?
5) Are/were they performing unreported work?
> I would say that's a pretty good indication what will happen with UBI - I'm sure there's loads of people who wouldn't leave their jobs because they like having more money(me included) but for a lot of people if free money is enough to get by then that's what they are going to live on.
Do you have children yourself? Children are a huge joy, but also a huge burden. It is a living hell to both work, and also have children. What some people with good wage do is work full time, both, and have child caretaker(s). Those are going to be employed.
There's also the problem that unskilled work in the West is in decline. I don't know if that is true for Poland though.
And there is the notion that you either work full time, or you don't work at all. Why these extremes? With 3-4 children you are overburdened by them, and it'd be an option for one of the parents to not work full time.