From War Girls by Janet Lee (page 57) :
"The Cadet Yeomanry shared space in the original FANY magazine 'Women and War' and was founded to teach boys from 12 to 17 years of age horsemanship , cavalry drills , elementary veterinary work , ambulance drills etc."
The badge/logo on the magazine cover appears (to me) to show CYC , so possibly Cadet Yeomanry Corps but the cap/collar badges in the original post appear to be simply YC .
Is it possible/probable that because they wore a First Aid (Red Cross) patch they initially wore a basic Yeomanry Corps badge until the uniform change in 1912 when the Cap badge changed to incorporate the Red Cross emblem ?