def child_age_string(birth_date):
    """
    Format a Child's age with a timeunit depth of 1.
    :param birth_date: datetime instance
    :return: a string representation of time since `birth_date`.
    """
    if not birth_date:
        return ""
    try:
        return timesince.timesince(birth_date, depth=1)
    except AttributeError:
        return ""

    Format a Child's age with a timeunit depth of 1.
    :param birth_date: datetime instance
    :return: a string representation of time since `birth_date`.
    
core/templatetags/duration.py