I think about 50% of kids who have imaginary friends choose for that friend to be an animal of some kind... it's a fairly typical wish-fulfillment scenario.

But Sam's got such a blend of practical and outlandish fantasy in him that...yeah. I think he wouldn't worry about the incongruity of a lion for a little brother at all.

It's all about modeling Dean's behaviour, even at this young age.

Anyway - glad you enjoyed it!