FatB,
棉花 is to clean pat pat, particularly for breast feeding mama, baby will do stool (大便)after each milk.
It's better to use baby wipe, (Johnson, pampers..etc) more convinient. If u prefer 棉花, u can get a pack from Eugene ('Ho Fa') which is cut (about 3"x3")already at around $5x which can last for 3-4 weeks.
The cheapest way is to buy 一大卷棉花, and cut it yourself but it takes time. REMEMBER to let the pat pat dry after cleasing or the baby will get diaper rash!!
I also go to 東區生!!