Anyone with kids (especially little boys) knows that holes in the knees of jeans comes with the territory. I've got a tip to make those jeans last a little bit longer!
Purchase iron-on patches and iron them on the INSIDE of the jeans at the knees. Have your child put them on, then slip a safety pin in the jeans just below where the knees hit - where they'll eventually get worn and make a hole. Then turn them inside out and use the pin as a guide to determine where to center the patch. Round the corners of the patch (which will make the patch last longer and keep the edges from wearing off). Take the pin out and iron the patch on. It will keep the knees of the pants from fraying into a hole without looking goofy because they have patches on them. They'll still wear in the knees, but not open up into a hole that gets bigger every time you have to wash them or every time your preschooler decides to crawl around on the floor. :)