What are the technologies that look like toys today but will be huge?

Drones carry video cameras today. Tomorrow they'll carry you, me, and everything else.

Car? As if. In 15 years, none of us will own cars. We'll hail an eDrone.

Agent based modelling already looks like a toy that isn't a toy. I think we'll see more and more of it as time goes on.

VR.

Fuchsia.

QR codes.

brain computer interface

There's something (multiple things, in fact) about Wordle that seems magical; so to your question, I think that small, free, respectful games that freshen and invigorate the mind and provide for entertaining social conversations will be huge.

In some ways they already are (outside the realm of technology) - but Silicon-valley-flavoured tech enterprise has tended to choose darker paths that eclipse those properties in favour of profitability and power.