Our son is 5 and he has worn these twice, which means they've been washed three times - once before he ever wore them, and then once after each wearing.  When he had them on the second time, he tripped and nearly put a hole in the knee.  He didn't hit particularly hard (didn't draw blood) and he was on dirt, as opposed to pavement.  When we washed them after that, there was a noticeable weak spot in the knee.  I think if he falls again, or even crawls across the carpet (playing with the dog, his baby sister, whatever), the knee will give.  It's hard to find pants that don't do this, so I will give it 4 stars because the rest of the pants look GREAT.  They fit well - he is small for his age (he turned 5 this Summer) and they're jsut a tad long, but sit well over sneakers, so they don't drag.  The adjustable waist is also super because he's pretty trim.  Overall, perhaps not the most rugged, but they look good otherwise, and they fit well, so they're still a pretty decent buy.