Since then, I've made him a few more pairs for this winter:
Today, I made him some polar-fleece track pants as pyjamas. They are super-easy to make and I took photos step-by-step to walk you through it. When I'm not taking photos of every step, they take less than an hour to make. The process is the same for making the slimmer style pants (above) or the looser-fit pyjamas.
Tracing and Cutting
First, find a pair of pants that fit (either loose or slim fitting, depending on the style you want to make).
Fold your fabric in half, right sides together. Lay your pants on top, inside out.
Trace around the outside of the pants, allowing room for a seam (about 1cm).
Make sure you stretch out the elastic when you are tracing at the top of the pants.
Allow room at the top to fold the top over and thread elastic through (about 3cm or so).
Cut out along the outline. Now you will have two pieces (that we will sew together to make 1 leg).
Fold another piece of fabric over, right sides together. Lay one of your cut-out leg pieces on top and pin it down.
Cut around the leg piece that you have pinned onto the folded fabric.
Now you will have 4 leg pieces, all the same.
Stitching the legs
Match up the pieces, right sides together, so that you have 2 separate legs. Pin along the inside of the leg and the outside of the leg. Sew these seams (I have used an over-locker, but a regular sewing machine is fine too - just sew a straight seam, about 1cm in from the edge, then finish the raw edge with an over-locking stitch on your machine).
Now it's time to sew along the crotch, so that the two separate legs are joined together. Start at the top of the pants, matching up the edges and pinning along the crotch. Once it's all pinned, you can sew it in a straight line from back to front.
Overlocking the top and bottom edges
If you are using a fabric that will fray (eg cotton), you will now need to use an over-locking stitch along the top edge (the waist) and the bottom edge (the hem). I didn't overlock mine, as I used polar fleece.
Attaching the elastic
Next, sew along the top to make a casing for the elastic. Fold the top of the pants over (about 3cm) and pin.
Make sure you leave a gap where you will insert the elastic. A trick I find helpful is to put a vertical pin where I want to start and stop sewing.
Measure the elastic around your child's waist and cut it to the right size. Attach a safety pin to the elastic.
Use the safety pin to help you thread the elastic through the casing.
Make sure the elastic is lying flat the whole way around the casing (with no twists). Overlap the elastic by 1cm and stitch it together using a zig-zag stitch.
Push the elastic inside the casing and sew the opening shut with a straight stitch.
Fold the bottom of the pants up about 1cm and pin. Make sure that both legs are the same length!
Use a straight stitch to sew the hem.
Cut off all the dangling threads and you have made a pair of pants! Yippee!
Here is Mr Sociable, modeling his new pyjama pants: