It's the "cross your arms" trick.
When you have a child who needs to be told something important, or reprimanded, especially one under say about 7, you have them cross their arms. It works especially well for older toddlers because it distracts them for a enough minutes to change their course of action. It also does a couple more things:
-It makes them look at you and concentrate on what you are saying.
-It makes their mood, somehow-I don't know how- change. Usually they get a little giggly.
-It makes them look really really cute, which makes you really really less angry.
I've been doing this for years and it works wonders.