Ah, yes, now I remember.
I had set up a makeshift neck-breaker in the living room: several pillows in a slant leading from the sofa to the floor, covered in a blanket, which they proceded to tumble down. And shout - let's not forget that things are always more fun with noise. Everything was running smoothly, so I went off to the kids' bedroom to practice guitar.
Several minutes later, Coco comes in holding an ice-cube to his eye and a cold-pack to his head, saying, "Daddy, I fell."
A huge wave of "Oh, shit"-guilt built up inside me and just as it was about to come crashing down in a bunch of hugs and sorrys and I-told-you-to-be-carefuls, he followed with, "April fool, dahahahaha, dahahahaha."
The "dahahahaha" is from SpongeBob, who introduced Coco to the concept. Then there was a bunch of laughter from the hallway, from the instigator.
Those kids are good.