Balloon Tank Puns

It was my son's birthday, and we were doing a Thomas the Tank Engine theme. Went to the party supplies shop, and one of the things we got for the party was a helium balloon with Thomas on it. Gave it to him, told him to hold on to it, otherwise it would float up into the sky, all the way to the moon as Peppa Pig phrases it.

Anyway, I'm looking around and I notice something weird... there are Transformers helium balloons, Peppa Pig helium balloons, Barbie helium balloons, Thomas of course, various superheroes... but I notice the complete absence of Elsa and Anna on these balloons. But Frozen must be the most popular theme ever for girl's birthday parties, I would have thought. So why no Frozen helium balloons?

I asked at the counter, and they told me that they used to have them, but they got too many complaints. Apparently every time a parent gave the balloon to a kid, she'd just let it go...