Kids will jump up on just about anything they see. If it can be climbed on, they’ll climb on it.
So when I put a bale of hay in the shed, the kids immediately begin jumping up on it.
I put a new salt block out in the pasture and the next morning it had muddy, poopy kid hoof prints on it.
The most energetic and nimble of them will climb onto the backs of their mothers.
In the past they wouldn’t have dared jump on Johnny. But now that he’s grown old and slow they climb on him too now. If he minds, he doesn’t show it.