Popplewell is the son of a barrister, Andrew Popplewell and Dr. Debra Lomas, a dermatologist. He was born in London. Popplewell has two older actress siblings: Lulu and Anna Popplewell. His paternal grandfather, Sir Oliver Popplewell, is a distinguished former judge. Popplewell had attended casual drama classes with "Allsorts Drama for Children".
Popplewell got his role in the film when his sister Anna auditioned for the part of Wendy; Freddie was the only one present to read the part of Michael with Anna, and he read so well that he was won the role of Michael. He was only seven years old when he got the part. He lost a tooth during filming. Additionally, he disliked when Nana had to lick his face while Michael was in the bath.