See these jeans? Way too far gone for a patch job.
Simply cut them off above the rips, making sure that both sides are the same length. Sometimes, if my son is around while I am doing this, I will have him try them on just to be sure, but this isn't really necessary. Save the bottom part of the legs for future patch jobs. (Or my mother-in-law says you can make a cute skirt for an American Girl doll out of them.)
I have been doing this for a few years now, and I have noticed that after the first wash or two, you will need to trim a few threads, but after that you will have a nice, clean, tiny frayed edge that is only apparent on close inspection. These make great little shorts for the boys to play in all summer.