If you look around you can find leathers that are shorter. I'm pretty sure that the childrens wintec webbers adjust to really short sizes, but I may be wrong. If you can't find something you like that's short enough, then just get a pair of normal 48" leathers, punch holes in the necessary places, and cut/have them cut down to the child's length. Provided it's not TOO long there's also nothing with having a fairly long piece of leather hanging at the end of the leathers if you just want to punch more holes in your current leathers.
For what it's worth I much prefer the thinner 48" leathers to the "average" length. I'm fully grown, but smallish