Measure the inseam of a pair of your child's pants that fit well. Then write the measurement on the itemized list (see last week's tip) next to the pants. Sizes vary so much from one brand to another, so this will help you buy only the pants that look nice AND will be a good fit for your child!
Make a list of what your kids need! Shopping at consignment sales can be overwhelming, so having a specific list that you can check off items as you find them is very helpful!