Find the right kids clothing size by age and height.
Children's clothing is labelled by age but cut by height, and the two diverge in most children by the age of five. US kids sizes step roughly every 2.1 inches of height from about 33 inches, so measuring and deriving the size is far more reliable than buying by the age on the label. European sizing is more honest about this — it is simply the child's height in centimetres rounded to the nearest 6 cm step, so a 117 cm child wears a 116. The months-until-next-size figure is the practical one for shopping: at a typical 2.5 inches of growth a year, a child moves up a size roughly every ten months, which is how long a garment bought to fit now will actually last.
Kids Clothing Size
US size = (height in inches - 33) / 2.1, rounded; EU size = height in cm rounded to the nearest 6 cm; months to next size = 2.1 x 12 / growth rate
Height. Age labels are an average and most children diverge from it by five or six, so a measured height gives a far better fit — especially for trousers and sleeves.
One size, sometimes. Beyond that the garment fits badly for most of the time you own it. A child grows into the next size in roughly ten months, so a size up buys perhaps six extra months of use.