It's All Our Fault.

Our two children were treated equally in every way right from the start.
Perhaps we overdid it, because now they compete with each other to wind us up to an extent that defies belief.
Who's card arrived first, which one did you open first, which one is the biggest/nicest, and so it goes on. It's all done as good fun and we are all amused by it. The two cards that came for fathers day are a good example, neither of them knew what the other had sent, so the similarity is funny.
Our son sent the one on the left with some beer, our daughter sent the one on the right with some chocolates.
We must have got it right after all.