I've caught two people practicing their art in Europe so far. They weren't very good and obviously needed the practice.
The first was a weedy little man who looked about 18. He was circling our group on a railway platform in Vienna. We were all facing each other discussing one thing or another. His intentions were very clear to me so I simply stood in front of him and stared at him. He looked rather uncomfortable, signaled to a friend down the platform, and then backed off.
The second was a teenage girl of about 16 who I caught with her hand in a friend's handbag just as we boarded a metro train in Prague. I think I actually slapped her hand away - don't exactly recall. Anyway, I scowled at her and she backed off, smiling sheepishly.
They seemed pretty incompetent to me.
That said we've been very careful, especially in busy tourist areas, and not had any other problems. I think the secret is to make other people look like better targets.
I haven't had anyone throw a baby at me either.