Winter

Sometimes you see a young child stopped in their tracks on the street. They're not running away or throwing a tantrum, but they stand still watching while their parent or caretaker walks ahead. It's such a small and harmless simulation of being left alone, but maybe it's be their first taste of worldly independence.
Mostly the kid is coaxed or smiled at gently to which they respond with a semi-far away stare. Mouth gaping, head tilted, twitchy-eyed, they're imagining what they'd do next.

It's a nice experiment because they're not in great danger and its a chance to get familiar with important feelings. And it's over pretty quickly because the kid realises they actually dont want to be without their mother.