Section 26A. Whoever, being a relative of a child less than eighteen years old, without lawful authority, holds or intends to hold such a child permanently or for a protracted period, or takes or entices such a child from his lawful custodian, or takes or entices from lawful custody any incompetent person or other person entrusted by authority of law to the custody of another person or institution shall be punished by imprisonment in the house of correction for not more than one year or by a fine of up to one thousand dollars, or both. Whoever commits any offense described in this section by taking or holding said child outside the commonwealth or under circumstances which expose the person taken or enticed from lawful custody to a risk which endangers his safety shall be punished by a fine of not more than five thousand dollars, or by imprisonment in the state prison for not more than five years, or by both such fine and imprisonment.