What length stirrup leathers for 10yr old child

I'm guessing you mean to buy? Can't say of the top of my head, but my 7 yr old is all legs & rides with stirrups around the same length an average 10 yr would.if no-ones got an answer for you by tomorrow, i'll measure hers tom morning for you.
 
You'd prob be after 48" ones, be sure to get 1" wide ones though. Some kids ones are terribly narrow out of thinner leather. I wouldn't trust them with my kid that's for sure!
 
Daughters are 34". Not got much growth room left in them though, got 2 spare holes, so I'd say go bigger. Also they're old english leather, not sure what weight the modern equivalent in that size could take.
 
Top