Legos.

Finn loves building with his big Duplo Legos. He makes giant towers of blocks.
Our job is to try to keep them from falling over while he builds,
since he hasn't quite mastered cantilevering and counterbalancing.

He builds them up until he can't reach the top.

J is trying to help out.

Almost tall enough!

And here's a short (45 second) video of the building process: