Heya guys-
To be brutally honest I am even more lost with modern kid's sizes than I am with modern adult sizes. When I developed these I went to K art and bought a bunch of kid's clothes, measured them and patterned our garments based on those sizes. When I sent the test batch out to parents, they assured me that garments were fab but the sizing was all wrong.
Although I list the 'KMart size', the failsafe way to determine if we have something to fit your child is to measure him/her. Here's what/how to measure:
Length- Measure from the top of child's shoulder to hem. Length given in chart is the actual length of the garment. Please allow for safe ground clearance, or hemming.
Sleeve- Measure from the middle of child's back to wrist.
Chest- Measure around fullest part. Measurement given on chart allows for 4" of ease between child's measurement and actual garment size.
Waist- Measure around point of child's tummy where his or her pants sit. Measurement given allows 3" of gathering at waist.
Chausses- Measure around fullest part of child's leg, and from high crotch to floor. Thigh and calf measurements allows for body ease. Inseam measurement given allows no ease.
Here are the tunic sizes:
Sizes: (measurements are- shoulder to hem length, spine to wrist, chest- allows 4" ease)
Small (28", 20", 25", roughly a 4T)
Medium (32", 22", 28", roughly a 6/7)
Large (37", 24", 30", roughly a size

If there's any other info I can provide, please let me know. I'm happy to help.
Gwen