The problem I have with this mainly has to do with the level of finish on it, and that it seems unrefined. Which sadly almost makes it look like some stock clipart.
Also, I think the colors aren't very good for this
They're very dark and saturated, and maybe not contrasting like mentioned before, but I can't say it's a very appealing overall look.
PS. the very bottom balloon is messed up lol. In fact, all balloons should always be facing upwards unless being pushed by other balloons.