I took my 5-year-old to the wrong birthday party. It taught me a lesson about the grace of strangers.

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• I was delighted when my shy kindergartener was invited to one of his classmates' birthday parties.
• Even though I didn't recognize the birthday boy or any other parents, I thought everything was fine.
• The people were friendly, and we had fun. A week later, I discovered we'd attended the wrong party.

My son, Bobby, had always been a shy person. When he started kindergarten, I was hoping he'd make a lot more friends.

I was delighted...