How can I stay serious ?!

How can I stay serious when this is happening?
Ok. Not exactly like the picture shows, but pretty close.
I'm washing dishes after dinner and Chris is on his laptop.
The boys are out in the breezeway playing.
I hear Cole crying and making a lot of noise.
I just assume he's playing around.
Then it gets louder and more intense.
Chris yells from the living room,
"Do you think you should go check on them?"
I reply, "I think they're just playing."
Then I pay more attention to the crying sound
and I realize that I've never heard Cole cry like this.
It sounds like a very panicked cry and a hurt cry at the same time.
I quickly turn off the water and run out to the breezeway.
I turn the corner and what do I see?....
Mason sitting on top of Cole's head with a big ole' smile on his face.
Cole is screaming in panic and crying flailing his arms and legs around.
Mason just sits there with his hands neatly folded in his lap and smiles at me,
then looks down at Cole's head that he is sitting on.
I bust out laughing and call Chris out there.
By the time he gets out there, Mason had gotten up.
Poor Cole. The first thing we say to Cole is,
"Why didn't you just push him off your head and get up?!"
He replies in between cries, "I couldn't! He was bouncing up and down
on my head and I had a hard time breathing!"
At this point, I feel bad for laughing and just standing there
watching while I wait for Chris to come see.
It's funny. If you had been here, you would have had a hard time
keeping a straight face too. Does that make me a bad mom?