"This kilt is too small ..." she said

[xman]

When you laid out the apron, did you add an extra inch to the fringe edge, and ditto for the underapron at the inverted pleat at the hips?

Yes and yes.

Is it the hips or the waist or both that are too small?

both

When you did the measurements, did you pull the tape measure tight, and did you measure over clothes or not?

Yes snugly. I did so because the PV kilts I have seem to be of these measurements. the heavier cloth is quite a difference.

If you lay the kilt out without stretching it, how close is the distance across the pleats at the waist and hips to the actual lengths you need?

Well now it's odd. I've taken new, looser measurements and STILL the difference is about an inch or so. That's an extra inch needed ABOVE the loose measurements to actually fit the boy.