I use the Toypedo to have FUN, while we work on (humming nose) bubbles.  My rule is that the child must be bubbling under the water the whole time, when he/she throws or catches this (we go under at the same time).  It's so much FUN, they don't realize they're learning/practicing rythmic breathing!!  It goes a LONG ways.  You have to be careful to get a good distance away from each other.  Kids throwing it to a friend close by can bump them pretty good with it!  When it sinks, we practice diving to the bottom (like a duck, head down, "tail" up!), with underwater arms & kicking!  FANTASTIC!!

We got this for my 2 year old for Christmas and he is still playing with it twice a week when we bring it to the pool.  He's made friends with all of the older kids (ages 5 - 15) who want to play with the torpedo too.