W. Va. Code § 44-10-10: When guardian to pay interest.

If any balance, whether of profits received or estimated, or of interest or principal, be due by any guardian, or other person acting as guardian, at the end of any year, which ought to be invested or loaned out within a reasonable time for the benefit of the ward, and the same remain in the hands of such guardian or other person, he shall be charged with interest thereon from the end of the year in which such balance arose, and so on, as often as such shall be the fact, during the continuance of the trust.