How tall is an average 5 year old?

the the size of a child's hand is 17foot wide.

Foolish answer.

From L.L. Bean:

(Gloves and Mittens)Measure hand length from wrist to middle fingertip. Measure both hands. Use the longest measurement to determine size.

"Sizing for: Cold Buster Waterproof Mittens

Hand Sizing (in inches) Size XX-Small X-Small Small Medium LargeFits hand measuring 4 4½ 5 6 7"

Hope this helps and hope the format remains.