Babies over 6 mos can get pretty active since they are rolling over, crawling, kicking, and pulling on their feet and putting them in their mouth. It can sometimes be a futile effort trying to keep booties on.
I still tried though.
However, they can sometimes still wear booties at that age. Especially if they are going in the stroller or out somewhere like church or visiting.
If you can make a pattern for ones that stay on that would be great.