Come and tell me about flotation aids - which ones are best?

[Tobermory]

Traditional blow up armbands or something else?
I have see disc shaped things, made of high-density foam - no idea of the name!

DD is fairly fearless, does some great kicking but not quite enough to keep her bouyant.

I liked them . And ds had a ball. At this stage that and him not sinking are my main concerns .

no floatation devices? swimming lessons that do without from the get go???