I think anyone with a boy between the ages of 4 and 10 (maybe older even) can bemoan with me all the holey jeans!! I think my son wore through 4 or 5 pairs since last September! So I got some tips from a Sister-in-law and started fixing. Here's how I do it:
Grab an old pair of jeans that are beyond fixing and cut a circle large enough to cover the hole/worn out spot plus some for seam allowance (very specific isn't it :) ). Then cut another circle out of iron-on interfacing.
Place the glue side of the interfacing to the right side of the fabric and sew around the edges about a 1/4" from the edge.
Trim the seam allowance to about 1/16".
Pull the interfacing from the jean fabric and cut a slit in it.
Then flip it right sides out and finger press the edges smooth (you don't want to use the iron until your ready to place it). Then press it onto your jeans.
Slide the pant leg onto your sewing machine and twist it so you can get to the right side closest to the seam. Set you machine for a tight"ish" zig-zag stitch and stitch over the edge as far as you can go around the circle. Then take it off the machine.
Turn the jeans around and put the leg back on, this time starting from the waist. Zig-zag, starting at the right side again, and overlap a few stitches at the beginning and end.