Run the air tubes up the back of your costume and possibly, under your wig, and connect them to the ears.. Run the opposite end of the tubes to a Y connector and connect the single tube to a blood pressure cuff bulb, hidden in your pocket.
Let the child "Beep" your nose and then squeeze the bulb

I hope this helps. I think it would be easier than trying to run the tubes from your nose to your ears.
Welcome to the board, BTW!