Do Ukrainian women sell children in large numbers in Poland? No, that's not true: Although there has been one instance of a Ukrainian woman called Svetlana, who did, in fact, traffic her 10 foster children aged between 4 and 16 in Ukraine, and later in Poland, when she fled there, there is no evidence of it being a widespread phenomenon.
The claim appeared in a video (archived here) on TikTok where it was published by @janostyak__ on May 17, 2023, under the title "So not the bad Russians this time?!". It opened:
A giant scandal in Poland. Ukrainian women sell adopted children. An article was published yesterday by Polish and Czech media. It reads that trade with Ukrainian children aged 4-16 flourishes, not just in Poland and that the described case is just the tip of the iceberg.
This is what the post looked like on TikTok at the time of writing:
(Source: TikTok screenshot taken on Mon Jun 12 15:28:06 2023 UTC)
The search for the phrase "Ukrainian women sell children in Poland", using Google News' index of thousands of credible news sites did not reveal any reports that this claim is, in fact, true, but rather that Ukrainian refugees in Poland are being exploited by traffickers.
According to Reuters as well as the Guardian, some Ukrainian women and children have become the victims of sex traffickers when fleeing the war through Polish borders. According to reports, there were instances where Polish pimps would exploit them for sex work. However, none of those sources indicated that Ukrainian women themselves systematically involved themselves in such activities.