The Duchess of Cambridge, who is royal patron of the charity, wore a blue tweed Missoni coat and midnight blue heels for the public appearance.
Kate spoke to the locals and chatted to schoolchildren as she arrived at the store in Holt, Norfolk, which is just over 20 miles from her home with Prince William and children George and Charlotte at Anmer Hall.
Kate, who has been patron of EACH since 2012, was taken on a tour of the shop by Tracy Rennie, EACH Director of Care.
During the tour, 11-year-old Rebekah Hughes, who suffers from a severe form of epilepsy called Dravet Syndrome, showed Kate one of her favourite items for sale - a silver purse.
"I'll have to buy her the handbag now or I won't hear the end of it," Rebekah's mother told reporters. "[Kate] was brilliant with Rebekah and it was a really special moment."
Kate cut a ribbon to officially mark the opening of the store and then went on an impromptu shopping trip.
According to reports, Kate purchased a Fireman Sam's Favourite Tales book and a Beatrix Potter Tom Kitten figurine for £10 for her son Prince George and daughter Princess Charlotte.
Try Reveal's digital edition on iPhone & iPad. Subscribe now & never miss an issue!