Guess what? I could only find one. Just one. Surely someone who designs patterns for tweens also loves this trend. There are actually a few for women. Burdastyle and the other big pattern makers have various culotte options for the home sewist. It is when you start looking for tween sizes, it gets more difficult.
What was the one I found? Well it is the Nina Skirt and Culotte by Compagnie M.. It is actually a Teen and Ladies pattern so it only comes in the upper ranges of tween sizing.
I have this pattern and I hope to sew it up before summer ends. If I don't get to it, then you may see an Autumn version in corduroy or wool in the future.
Now it was not exactly true that this is the only pattern. There are a few vintage patterns available out there on Etsy and other sources of various lengths of culottes.