Can you take a pic? Could be an injury, but seems weird it's on both sides. Is there somewhere the horse might have squeezed through and caught on both sides, or been stuck trying to climb through a fence/poles. Is it the same place on each side or could it be two kicks at different times (horse herd changed, new horse?)
What does the soil/sand look like that the horse is lying down on and does your horse spend a good deal of time lying down? Could be parasites in the soil?
Are they infected (smell, colour of oozing?).
If they are not infected then hose daily with clean water to keep clean and encourage good tissue healing, if infected you will need to give the horse some penicillin and possibly some antibiotic ointment.
Does your horse have a blanket? It may be a strap rubbing as he rolls and gets up which is keeping it raw?
Horses are pretty good at healing themselves if given the right environment but if you suspect it's infected, you may need to medicate.