My husband had a pair of gardening pants which he had worn out at the knees. He asked me if I could mend them. So I decided to visit the dollar store to see if I could find any knee patches. I couldn't find any, but wandered over to the kitchen section and found pot holders (two for $1.00).
This page contains the following solutions.
Save the fabric when you turn a winter long-sleeved shirt into a summer short-sleeved shirt and use this fabric to patch the knees or add length to kids pants. The shirt can then be worn with the pants as a cute matching set!