Apparently, it was the first time they played the game (that morning). As in, first time ever. According to CO. No rules, no 'usually'. imo
"Then he got bored and decided to play another new game called Daddy Tiger.
He hadn't played it before. I suppose it came from Mummy Monsters. He [was] pretending to be Daddy Tiger."
Missing William Tyrrell, Caroline Overington, Chapter 2
She says that at first he was crawling around on the ground, then a bit further on she says that he started jumping off the patio and roaring, running around the corner and coming back ... until he didn't.