Serious Post: How do you avoid “hiding” that a child is adopted?

This may seem like a silly question. But, my brother and his wife are considering adopting a child.

My brother’s wife was adopted, and her adopted parents didn’t tell her until she was 23. She was devastated. Even more so when she found out her birth parents passed away only recently.

How do you tell a small child that they are adopted? How do you say it without hurting their feelings? Should you casually remind the child every few months? Do you show them a video from when they are adopted in a video every birthday?

Thank you,