These are the perfect pants for plays such as Oliver, Into the Woods, Beauty and The Beast and Mary Poppins, but unfortunately (or fortunately depending on when you were born) these have not been available in the shops since I was a New Romantic (shh, don’t tell anyone and I promise not to share my photos!)
Luckily for you, they are actually quite easy to make from an existing pair of pants, so here are the steps to follow. I recommend corduroy or wool (not denim, it wasn’t invented until 1853).
Here are a few tutorials on how to convert pants into knickerbockers, if you can sew.
Non Sewing Method
If you don’t sew, or don’t want to cut the pants up, you can “convert” a pair of pants by tying a piece of elastic just below the knee (you can use hair elastics) and puffing the pants out a bit around the knee so the elastic doesn’t show. Tuck the rest of the pants (below the elastic) into long socks.