In response to some questions, and after using and abusing these chaps for a year, here are some updates:
First, this pattern assumes that a) you know your way around a sewing machine. It is not a hard project, but I don't explain how to thread your sewing machine, for example. b) that you are comfortable "winging it" with play costumes. As you can see from the photo, I didn't make anything exact or perfect.
Second, the velcro tabs work great to close the legs. However, not so great at the waist. I ended up replacing the belt with one from a thrift store that I cut down to my toddler's size. He is working on buckles anyway, so it is good practice, and the velcro buckle was not holding. Ditto the velcro tab for the lasso. I would definitely replace velcro with a snap or a button - however, my son isn't really that into the lasso, so in the end I just cut that tab off.
Good luck! Link to a photo in the comments!
In making costumes, even for toddlers who wear them everyday, I'm not one to get too precious or make sure that every stitch is perfect. In my recent experience with my 4-year-old, costumes are a favorite for a few days, and sometimes get recycled a month or even a year later. The obsessions seem to come and go quickly. Heirloom-quality they do not need to be.
Costumes for pretend play - whatever the obsession - do need to be a few things. They need to be simple to put on "by myself." They need to be comfortable. They shouldn't have certain pieces that "have to" go a certain way - because most toddlers seem to be tinkerers. J came to me with the chaps completely dis-assembled in about 5 minutes - mostly because he wanted to see how everything worked. So this pattern doesn't have a lot of fussy things, uses velcro, and can be completely taken apart and put back together without undoing all your work. It also folds up small in our dress up suitcase!
You will need some other accessories (not shown here). Jeans are good, although any plain trouser pants work too. A flannel shirt will work if you don't have a western one with those fancy pearl snaps (but oh, my J would love one of these). A neckerchief (a red triangle of fabric will work). A hat (but of course). A vest is optional in my opinion. Cowboy boots, or any boots. You will see that these chaps come with a lasso. Here is how to tie one. Ours is made of inexpensive sisal rope from a home improvement store.
Ready? Let's go rope some dogies.
Here is the end result, so you can keep this in mind while we go through the steps. Some of the pieces look a bit weird, but it will all work out! I recommend reading through the whole tutorial first to come to grips with the ideas before cutting.
You will need about 1/2 a yard of chap fabric (I used brown duck cloth, you could use pleather, cow-patterned fleece, whatever you fancy); a scrap of buckle fabric (I used yellow felt); velcro, and sisal rope for the lasso.
Here are the pieces. I measured everything against a pair of jeans that fit my 4 year old. The belt is 24 in by 4in. The tabs are about 6 in long.
The violin-shaped chap pieces are as long as his jeans plus 2 in for turnover at the top. The chaps need to be the width of one pant leg, since they are going to "wrap" around the outer part of the leg and fasten around the inside with velcro'd tabs. I just eyeballed the shape - draw a curve down to the crotch for the front and back, then another slight curve in at about the knees on your kid's jeans. Round off the bottom. Trust yourself. They don't have to be perfect, they just need to be evocative of the wild wild west!
Here is the belt. Fold and press in half lengthwise, then fold and press the raw edges in to meet at the center and re-press in half. Stitch down the fold and close in the ends. Alternatively, you can use an existing belt, even one with a big fancy cowboy buckle. If you do, make sure that your chaps have a deep enough tunnel at the top to thread the pre-existing belt through.
Next, fold 1/4 in down on the top of the violin pieces. Serge or zig-zag the curvy edges all the way around, catching in the top fold. You could also hem all around but who wants to fuss with all those curves? If you use fleece or pleather you don't even have to finish the edges! Skip all the zigging and zagging! Why did I even use duck cloth?!
Next, fold down your tunnel for the belt to run through. Mine is about 2 in. Stitch down the fold over as shown above.
Your violin pieces will now look something like this. Lay them out wrong-side up with the rear seat together, as if your toddler were going to lie down face up on them to try them on. At least that helped me visualize how to lay out the tabs, pocket, and lasso loop.
Next, the pocket (on the left chap). I don't know if this is traditional, but it seemed to need something to compensate for its lack of lasso. I just serged the edges of the pocket and hemmed the top, then topstitched down. You could get fancy with the stitching here if you are that sort of person.
Here is the lasso loop on the right side chap. I folded a small tab and stitched it down the center, attached half of a velcro tab to one end, positioned it just below the belt tunnel on the right side out of the right chap, and sewed it down. I topstitched on the other half of the velcro where I had sewn the loop to the chap. To use the loop you just close the two velcro pieces together. You can see below how it will hold the lasso within easy reach of the right-handed.
UPDATE: having seen some heavy use, I have replaced the lasso loop fastening with a heavy duty snap. The velcro came undone too easily.
I imagine you mothers of the left-handed are used to modifying stuff like this for your south-pawed - one of the good things about sewing your own, right?
Now for the tabs to hold the chaps around the legs. The photo above shows you the positioning looking at the chaps right side up threaded on the belt for wearing.
The tabs are positioned on the bumps around the thighs and the calves. Fold the remaining 4 tabs in to the center lengthwise and topstitch to secure. Stitch half of the velcro to one end of the tabs, as shown.
Sew the non-velcro tab end to the bumps running down the rear of the violin piece. When the chaps are on, your kid is going to reach through his or her legs, grab the tab, and velcro it to the front of the chaps at the thigh and calf. The picture below shows the tabs and velcro on the right chap (the one with the loop for the lasso)
If you have a real belt with a real buckle you can use that now - just thread it through the left and right chap appropriately and toss the whole thing to your cowboy or girl.
Here are the chaps, tabbed together and laced up, viewed from the front.
I suppose it is a measure of the success of this costume that all action photos of the whole ensemble (plaid shirt, neckerchief, hat, jeans, boots) are too blurry to show!