mieć coś w planie in English:

Let's take the train-I don't think I'm up to driving so far. The children must be up to sth-they're very quiet.

1. I don't think I'm up to driving so far. 2. The children must be up to something.

The children must be up to something.

We start tossing a coin, and we get a head -- and you start sitting on the edge of your seat because something great and wonderful, or awesome, might be about to happen.