When looking for a new dog, how can you tell what temperament a puppy is going to have as an adult dog?

My son and his wife may be in the market soon for finding a new family-friendly dog.

I’ve picked out two dogs in my life. All I did was sit in the middle of the litter and wait. Which ever one came to me first, and wanted to curl up in my lap was the one I took. I had good luck with both dogs when they became adults.

However, I’m pretty sure I was gauging other aspects of the puppy’s personality in some way, but I’m not really sure how.

How can I tell them what they need to look for in a little pup?