A.F.
Dear C.,
It was always advised that you buy new shoes for every child, because using old ones can cause exactly the problem you're describing. They way I handled things was, I would only pass along shoes that my kids have worn fewer than 10 times. Things like formal shoes, that they only wore once for my sister-in-laws wedding. Or speciality shoes like beach/water shoes. All other shoes I tossed in the trash because I knew that no one should wear them. It is a bit easier when you pass the shoes among siblings because there you know exactly how often they have been worn. I hope this helps. A.