An ideal gas mixture filled inside a balloon expands according to the relation pV ^2/3 = constant. The temperature inside the balloon is 

$p{V}^{2/3}=\text{ constant }$

$\therefore \left(\frac{T}{V}\right)\cdot V^{2/3}=\text{ constant }$  (Using Charles' law)

$\text{ or }T{V}^{-1/3}=\text{ constant or }T\propto V^{1/3}$

So, with increase in V, temperature T will also increase.