Some of my clients have their parents listed as primary or contingent beneficiaries of their estate. This may be a purposeful decision, or it may be because they named the beneficiaries many years ago before they had a spouse or children, or because their parent would inherit if a spouse predeceased them.
Unless having your parents as the beneficiary of your estate was a purposeful and thought out decision, you may wish to check with them about having them possibly inherit from you.
There may be tax ramifications for them that they wish to avoid, or if they are in a nursing home on Medicaid when you pass away, an inheritance could inadvertently affect their eligibility.
Speaking with your parents, and maybe even coordinating with their attorney, would be the best course of action if you want to list them in your estate plan.