Our sizes tend to run a little closer to age than the ones in the store.  I've often found I need to purchase a store size 8 for my five year old - mainly for the length - whereas I can make a size L (3 - 5 years) and know it will fit.  I have personally found the sizes to be fairly generous.  Although the new dresses I make for my 12 year old are all in the XXL (10 - 12) size, she has been known to pull out her older dresses (XL - 6-8 size) and they are still not too tight.  On the other hand, there have been rare ocassions where a customer has ordered the XXL size, only to be disappointed when it was too tight for their 11 year old daughter.  Therefore, I have put together a chart of measurements for each size.  Please NOTE:  The measurements are measurements of the garment.  They are not measurements of the child.  If your child's chest/waist measurement is exactly the measurement in the chart, the dress will be too tight.

The chart can be found here:  http://www.daddys-little-princess.com/sizing.html