As well as being great fun, blowing bubbles helps beginner flute players develop the embouchure (lip shape) required to make their first sound on the flute.
Blowing a long continuous stream of bubbles also helps develop control of the air stream and column of air required to play a longer held note on the flute.
Simply blowing air through a straw helps show children the size of the hole in the lips required to make their first sound on the flute.
Blowing bubbles in water through a straw not only shows the beginners the size of the embouchure hole but also helps develop a steady column of air and air pressure needed to help get their first sound on the flute. Great fun too!