How This Is Us cast its breakout young stars

The Hollywood Reporter

"You have to look on multiple prongs,” says casting director Tiffany Little Canfield. “Do they resemble the characters that have been established already? Then, do they play the age? Often with kids, you do a little bit of a range of age. You don't just say they have to be 7, because every 7-year-old is different, every 8-year-old is different, every 9-year-old.”