We don't know if DB bought the baby food/wipes at all. It may have been her 20 year old brother who bought the baby items. Does he have a baby, I wonder?
Another poster in the "facts" thread is reporting that two separate purchases were made... the baby items and the wine. DB walks out with the wine. The brother is holding a grocery bag. Are the baby items for his child?
Not sure how to answer that avoiding the "family sluething" thing. There is no indication I've run across that he has a child of his own. No court ordered support, no marriage, no girlfriend with a baby. What is possible isn't necessarily likely, as you well know. He could be buying the items to donate them to the local women's shelter or food bank. That's possible too but unlikely.
Occams razor says the lady with the 10 month old baby buying everyday baby needs at the market, is buying them for herself.