设计时间类Time和日期类Date，Birthtime类由Time类和Date类派生，并且增加一个数据成员Childname用于表示小孩的姓名，编写程序输出小孩的姓名和出生时间。

下面是时间类Time的实现：

class Time:
    def __init__(self, hour=0, minute=0, second=0):
        self.hour = hour
        self.minute = minute
        self.second = second

    def __str__(self):
        return "{:02d}:{:02d}:{:02d}".format(self.hour, self.minute, self.second)

下面是日期类Date的实现：

class Date:
    def __init__(self, year=0, month=0, day=0):
        self.year = year
        self.month = month
        self.day = day

    def __str__(self):
        return "{:04d}-{:02d}-{:02d}".format(self.year, self.month, self.day)

下面是Birthtime类的实现：

class Birthtime(Time, Date):
    def __init__(self, child_name, year, month, day, hour=0, minute=0, second=0):
        Time.__init__(self, hour, minute, second)
        Date.__init__(self, year, month, day)
        self.child_name = child_name

    def __str__(self):
        return "{} was born on {} at {}".format(self.child_name, Date.__str__(self), Time.__str__(self))

现在可以测试一下Birthtime类的功能：

birth_time = Birthtime("Alice", 2021, 8, 1, 10, 30, 0)
print(birth_time)

输出结果为：

Alice was born on 2021-08-01 at 10:30:00

这个例子展示了如何使用继承来创建新的类，并且如何在子类中调用父类的构造函数。