I saw this anime movie in the early 2000s and unfortunately I don't remember much. All I really remember is that it revolves around a bunch of kids that go to an abandoned city/town and they have to wear masks. The city/town is full of spirits and if they see your face they take you. I don't really remember much more and I'm not entirely sure if this plot is accurate to the show I'm thinking of. I've been looking for awhile now and no luck. Please can anyone help me.
It should be "Kakurenbo" but it had been released in September 2004, premiered in March 2005 if you consider it early 2000s.
In Kakurembo; there are children who wear masks to play hide and seek near an abandoned town. They wear masks because children who play the game disappear (believed to be taken by demons), and they believe these masks will protect them against these.