Children's pirate costumes are very popular at fancy dress parties with the main influence coming from films. It can be very easy to put a costume together for not very much money. A very simple method for a boys outfit would be to use the child's old trousers, cut them off just below the knee and make it with a jagged edge.
This gives it an old appearance. Next take an old white blouse or shirt and add a waistcoat over the top. You can opt to put a thin piece of fabric around the waist for a belt to bring the outfit together. Long socks and pointy shoes or boots would look good with this. An eye patch and a bandana would complete the look.
There are more options if you are female. You could either wear the trousers outfit or you could go for something more feminine such as a dress or skirt and top. Whichever you pick ensure the bottom of the skirt is jagged or a handkerchief hemline for an older effect and you could also get away with a boned top.
Use face paints to make it look realistic. Smudge dark brown faintly into spots or smear lightly over the whole of your face. Children would wear pretty much the same sort of outfit that an adult would wear, in that you can go and buy trousers to cut up quite cheaply, use one of your own shirts on a child as it will be nice and big.
Older girls and women can usually utilize something in their wardrobe for use as an outfit, a shiny party skirt with an uneven hemline would be ideal, this could be either stripey or shiny or even plain black. Fishnet tights and mid calf boots would compliment a more grown up look. You can then start to add items such as hats.
So as you can see there are plenty of options to look at when trying to put together pirate costumes. Whether you decide to buy one from new or you find clothes or borrow them from others to complete your look, it is a very easy costume to put together for very little money, and one that you can make look really realistic.