Alright, I'm assuming SOME sewing knowledge here which I'm sure you guys can handle. If there's any questions you can feel free to email me and I'll do my best to clarify.The first step is to take an existing pair of pants that fit well. Ideally, these will also be pj pants, but if you use something like a pair of jeans you could just allow extra seam allowance.
Fold your pants in half. There's a little notch in the butt area. Make sure that is pulled out. Place your pants on the fold of your fabric like this:
You will cut along your pants, leaving a seam allowance. Leave extra room at the top (about an inch and a half) for the casing and an extra inch on the bottom for the hem. Your butt area probably draws in quite a bit. You'll need to account for the elastic though, so I do mine almost straight up. My child also has a little extra junk in the trunk if you know what I mean. If you or your child is on the less endowed side you'll be able to taper in a bit more.
Here's my pants after I cut the first leg. I allowed extra room because these were last years pants and the little one grows like a monster! You'll need to cut another leg exactly like this! Don't forget to place it on the fold.If you use a serger you can serge the bottom edge of your legs now. If not, you can just fold it over an extra time when you hem.
Then, fold your leg in half placing the right sides together. You will sew up the lower leg ONLY. I serge but you could also zig zag or use a french seam. Stop when you hit the butt notch. (Yes, I am officially naming it the butt notch.) In the picture below the thin blue line indicates the top, or the waist. The arrow indicates where you should be sewing. Do this to both legs.
Here's where it gets a bit tricky to explain. Turn one leg right side out. The right side out leg should be placed INSIDE of the inside out leg. Essentially the right sides of the legs are together. Line up your edges. It should like this:
Sew your edges together. It will be like sewing a large "U" shape. You can serge or again you can zig zag or whatever you're comfortable with. After that I remove the leg from inside of the other leg. The pants will be inside out. I reinforce all of my seams with just a straight stitch. I also serge along the waist.
Hem the bottoms- if you zig zagged or serged you can just fold the edge over and straight stitch it down. If you didnt or you want a more finished look, you would fold your bottom once and then again to hide your exposed edge.
You're almost done! All you need to do now is to create your casing for your elastic. I like to use 1" pajama elastic. The absolute easiest way its to start with a long length and simply fold your fabric over the elastic as you sew.
Once you get about a half inch from where you began back stitch a bit and then remove the fabric from your machine. Tighten the elastic to your desired length. plus about an inch and then cut it. Sew your ends together and tuck them back in the casing. stitch over your hole and you're done!
If you don't have enough elastic to do it that way or your want a more finished edge you can fold over your top just a bit to conceal the edge and then fold it down about an inch and a quarter and sew it down leaving a small opening to insert your elastic. Feed it through with a safety pin and finish as described above!
Now, shamelessly chase your toddler around with a camera while she models the new pants. Give up when she hides in her bunk bed.
I know I dont explain things the best, so like I said, please don't hesitate to contact me if you need more help!