The 41-year-old actress - who has Maddox, 15, Pax, 11, Zahara, 12, Shiloh, 10, and eight-year-old twins Vivienne and Knox with her estranged husband Brad Pitt - was spotted in the unnamed bookshop in the English capital on Monday (13.03.17) where she was joined by her daughters Zahara, Shiloh, and Vivienne, as well as one of her sons who was not identified by the onlooker.
According to the source, the brunette beauty bought around "30 books" for her children, including a book from the 'Harry Potter' series.
The onlooker said: "She bought about 30 books. Mostly colouring books, a 'Harry Potter' book, plus some book markers and Easter-themed project books.
"She was talking to the girl at the counter about how she loves to get her kids to enjoy books and loves London, as there are so many good book stores."
And the source said the 'By The Sea' actress thanked them for being "considerate and sweet" as they allowed the family to take the last available copy of the final book in the J.K. Rowling fantasy series 'Harry Potter and the Deathly Hallows', and said the family were "nice people".
They added to People magazine: "She also thanked me for being considerate and sweet for letting her kid have the last copy of the 'Deathly Hallows'. It was in my hand at the time, but I let him have it.
"She was lovely. Her kids are so polite. Her lad came over and thanked me for letting him have the book he wanted for a school project. Called me 'Sir.' Nice people."
It's not the first time Angelina's children have been praised for their good behaviour either, as her eldest son Maddox - who was adopted from Cambodia when he was a baby - was praised by author Loung Ung for being "kind and generous" whilst helping out on the set of Angelina's new movie 'First They Killed My Father'.
Loung - whose book about the Cambodian genocide inspired the movie - said: "I have watched the young people grow into really kind, empathetic, curious human beings.
"Pax is a talented photographer and Mad is so kind and generous. The cast kids, they all looked up to him as a big brother."