It's indeed a discovery Madoka has already made.

But she doesn't want to point that out to him. She doesn't want Devero to feel bad - especially since Madoka has figured most adults feel kind of bad when kids grasp something quicker than they do. So she's quiet for a moment, trying to figure out the best way to go about it, the way that won't hurt Devero's feelings in the slightest--

And then she's got it.

"Do you want to try? I kind of have my hands full, so.."

The perfect excuse. Madoka's feeling pretty clever now.