We have tested our software on children as young as 4 years old. This works relatively well. Major preprocessing and registration issues arise when you’re working with images of neonates where T1 contrast of grey and white matter is flipped in comparison to adult T1 images.
If you’ve tested SVReg on your subjects and still believe that a child atlas is needed, you have the option of modifying the labels on one of your subjects and creating your own custom atlas using the module svreg_make_atlas. Directions can be found at the bottom of the page: http://brainsuite.org/processing/svreg/svreg_modules/