As the owner of the property, you are liable if the kids or the lawn service man are injured on your property. Your liablility for the kids' injuries would include compensation for their medical bills and compensation for pain and suffering, which is an amount in addition to the medical bills.Your liability if the lawn service man is injured on your property would also include compensation for the medical bills, compensation for pain and suffering, and compensation for wage loss.If anyone is injured on your property, refer the matter to your homeowner's insurance carrier.You are correct that it is advisable to hire a new lawn service  where kids won't be operating the equipment.