I talked with my friend on December 29 2020. Then I talked with him again on January 03, 2021.
Q: What was the year when you last talked with your friend?
Q: And what was the year the previous time you talked?
Comment: So dutifully doing the arithmetic, $2021\, (-) \,2020 = 1$. This means that 1 year has passed right?
This is an almost universal joke around the change of the year ("it's been a year since we last talked", etc). But how to explain this to a little child?