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DIY lengthening kids pants sewing tutorial

Try this DIY lengthening kids pants sewing tutorial to make pants last longer! Perfect for mending hole-y knees or just adding length.

If you’re looking for creative ways to add length to pants, here is an easy sewing method! My eldest loves these bat pants, but not only were the knees completely threadbare, they were looking more like capris than pants with his ankles hanging out. I decided to take care of both problems at once by chopping out the knees and replacing them with a larger segment!

Beginner friendly, keep reading for a DIY lengthening kids pants sewing tutorial that shows you how to do the same thing! This would work well for adult pants too.

knee mending tutorial

Here you can see how dire the situation was! Practically a window at this point. It would be easy to make the new knee quilted, add fun appliques on top, etc. The original bat pants are from H&M so not exactly super high quality. I don’t think the rest of the pants will last longer than another year so I didn’t want to invest a ton of time into them knowing they won’t be handed down again, so mine are boring plain black.

If you like this post, check these out while you’re here:

how to make kids pants last longer

Here is what the finished pair looks like! The edges are left raw in this tutorial, so this would only work for knit pants like leggings or sweatpants (not jeans). I happened to have another hole-y pair of sweatpants on hand to chop into, but you could also very easily DIY the insert piece with fabric yardage as well.

Pin this DIY lengthening kids pants sewing tutorial with this link or image below:

creative ways to make pants longer

Ready to try it yourself?

DIY lengthening kids pants sewing tutorial


  • Rotary cutter [Shop: Amazon ]
  • Acrylic quilt ruler [Shop: Amazon]
  • Sewing machine
  • Ballpoint needle [Shop: Amazon ]
  • Sewing clips [Shop: Amazon ]
  • Extra pair of semi-similar sized pants that are a similar weight or fabric yardage to DIY the new knee


step 1 making pants longer diy

Step 1- First, you need to slice off the offending knee if you’re working around a hole like I was – otherwise just cut wherever you want the new section to start. Match it to the other leg for an identical chop.

step 2 making pants longer diy

Step 2- Next, I compared my sliced piece to the existing pair of sweats I had. The bat pants are a kids 12 and the black are an adult small – it worked out fine, just trying to match up widths before I cut the new knee. If you want to be careful, you can mark top/bottom and front/back with a pin or chalk here – I think with baggy-ish sweats it doesn’t matter as much but maybe it would on some styles that have significantly more fabric on the back leg piece or something.

step 3 making pants longer diy

Step 3- The most important step of this is *right sides together*. You’ll want to flip the new knee inside out, matching side seams, and clip all the way around. 

step 4 making pants longer diy

Step 4- Time to sew! Don’t forget ballpoint needles with knits and to use a stretch stitch unless they’re super baggy. Pull off the free arm if you have one and slowly sew around the opening. I used a 1/2″ seam allowance, which is large, so both feed dogs can grab the fabric no problem and top stitching will be easy. Then, pull it off and press the new seam allowance you just created up into the knee and top stitch it down.

step 5 adding knee patches

Step 5- This is what it should look like now! Repeat on the other leg!

step 7 adding kneepatches kids pants

Step 6- Turn the lower leg inside out and nest inside the new top leg piece, clip and sew the same as previous steps. Repeat for the second leg and you’re done!

knee replacement sewing tutorial

Here you can see how much longer they got, with the old knee layered on top!

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Muhammad Asim

Wednesday 19th of July 2023

What a brilliant solution to the problem of hole-y knees and pants that are too short! I appreciate the detailed tutorial and the clear instructions provided. It's fantastic to see how a simple sewing technique can extend the life of kids' pants. This DIY method is not only practical but also allows for some creative customization. Thank you for sharing this helpful and inspiring tutorial!

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