During a high-spirited shopping expedition Sunday, Angelina Jolie – who plays Sleeping Beauty's evil queen in the upcoming live-action Disney movie Maleficent – and three of her six children with Brad Pitt hit the Halloween Adventure Superstore in Sherman Oaks, Calif.
"Halloween is a big deal for the kids. There are decorations everywhere at the house and the kids are already dressing up," a family source tells PEOPLE. "They will have a party at school and will also go trick-or-treating with their friends on Halloween. The kids are all very excited."
Picking out costumes and other holiday-appropriate items with the mother were Shiloh, 6, and 4-year-old twins Knox and Vivienne.
"They spent almost an hour at the store in the morning," according to an observer in the store. "Angie looked gorgeous and was very sweet. The kids were excited and very adorable. The youngest ones were very into all the costumes, and the older kid seemed more into the Halloween decorations."
Added the observer: "Despite all the excitement, the kids were very well-behaved, and Angie was great with them. She smiled at their excitement, but was at the same time good at saying no. The kids would have left with everything in the store if they would have been allowed."
In the end, said the source, "Angie only let them pick out a present each, but the kids seemed very pleased with their picks." In Shiloh's case, it was a pair of sunglasses, while "Vivienne left the store in a pink unicorn costume, and Knox clutched a plastic alligator toy."
A photographer said, "Vivienne looked adorable in her unicorn costume, and she seemed very excited that she got to wear it out of the store. Knox was in his own world with the toy alligator, and Angie had to pick him up on the way to the car so he wouldn't get lost."
Taking her role as older sister seriously, "Shiloh acted like Angie's big helper and she took care of Vivienne when they walked back to the car after the shopping trip," said the photog.
And although they weren't along for the shopping trip, Maddox, 11, Pax, 8, and Zahara, 7, were not overlooked. Their mother, said a source, found toys for them – including a gothic count costume, a count makeup kit, decorative plastic spiders and a sprayable spider web.