It takes very little fabric to make an item, it is fun to do and results in a unique garment not found in any store. It is important to remember who you are sewing for. Involve the child as much a possible from selecting a pattern to deciding on what type of fabric to use. There is nothing worse then spending time and money on a item which will never be worn. When shopping for fabric, don't compromise.
Children are especially hard on their clothing.
The fabric has to hold up to constant wash and wear. There are many different fabrics on the market today so be sure and ask about the durability of the fabric including the possibility of shrinking and fading. Most of the time it is better to pay a little more for a fabric that will give you years of wear and still look great. When you arrive home with your new fabric, pre-wash and dry it if necessary. This way, when you have a few moments you can start your project right away without waiting to wash and dry the fabric.