For the purpose of income calculation under paragraph 1, if a lawful child who is a minor derives income and the marital status of the parents exists throughout the tax year, the income of the child shall be treated as income of the father. However, if the marital status of the parents does not exist throughout tax year, the income of the child shall be treated as income of the parent who exercises parental power, or of the father if both parents jointly exercise parental power.