Hello Sofia,
If I am not mistaken it is the LM386 which directly interfaces with an 8ohm speaker, through an electrolytic capacitor to decouple the DC.
A better alternative would be the electromagnetic buzzer which is around 12mm in dia which is available in 3V, 6V and 12V etc.It is simple to drive with a port pin and a transistor.They are also available with a built in oscilator/driver.
Regards,
John.