Second hand clothes are part of the "green" trend! There are a variety of ways to purchase clothes, not only for yourself but for your children. I know that people may feel strange sometimes buying something that isn't new, but it isn't much different than a hand me down from a friend. Most places that offer second hand clothes, have certain standards for accepting the clothes and inspect everything they take in.
For myself, I love to look for something vintage, designer or unique. Second hand maternity clothes are a great way to boost your wardrobe without breaking the bank too! There are also lots of cool accessories you can find at shops as well - like handbags and costume jewels.
For my family, I have found some almost new pieces that have worked great. Kids outgrow their clothing so fast that the clothing may have only been worn a handful of times. Items that are normally more costly, like coats, sweaters or dresses, can be found at a fraction of the price. Some places even have items that still have the tags!
To start, I would suggest you find a store and visit it. Once you see the items you may then feel more comfortable expanding to some of the online options.