The weather, your health, and your vacation schedule do not mean anything to your horse. Horses cannot teach responsibility to children, they can only help parents teach responsibility. Responsibility for a child's horse always falls to the parents. The horse owner must purchase everything else and provide the labor. Fencing is in constant need of attention.
Bedding needs to be changed daily.
Places to store feed - grains need to be protected from molding and rodents. The average horse needs farrier care every six to eight weeks. Regular worming - every six to eight weeks. Regular veterinary care - seasonal vaccinations. Some can be administered by the horse owner, others require veterinary certification.