Help to find a really short story about small boy from large family who made a really simple device (IIRC it consisted of tin can and two paper circles) which could make things disappear if you look at them through it and blink. Some other points I remember:
- First thing he made disappear was cat
- He did't invent the device but read about it in a little sister diary
- Said sister told that she knows how return all items and requested some stuff. In the end all that stuff was actually just something she wanted for herself.
- She has destroyed golden watch for "dramatic moment"
- In the end she just told that all items would return exactly 7 days after disappearence, as boy built 7-days version of the device
- She mentioned that she tried to make longer-working version of the device, but couldn't because it requires blood from a heart of young boy, and her little brother screamed too much when she tried to make a cut