Just one more thought. There's one other significant issue to consider when thinking about how long you can make a kilt last for a child by moving buckles and letting down the hem. If you've made a kilt for a girl in late grade school or early middle school, you need to be prepared for the fact that her shape will change significantly. Change in the waist/hip proportion will mean that the kilt will no longer fit in the hips, even if it fits in the length and waist.

The advice that I give most people is to sell a kilt that no longer fits well, rather than to take it apart for alteration. A well-taken-care-of kilt that has never been altered other than to raise or lower the hem will have a higher resale value than one that has been altered to fit a changed shape.