At 10, Grace Morgan is a young fashionista and takes pains to dress in the latest styles. But her mom, Amy, works part-time and her husband was recently laid off, leaving little room in the family budget for designer-brand clothes.

So Grace didn't ask her mom to open her wallet this fall to buy clothes. Instead, she sold a stack of her own old jeans and shirts at a rummage sale and paired the proceeds with discount coupons to get the stylish jeggings and tops she wanted for school, says her mother, of Lake in the Hills, Ill....