Thank you very much for playing my game and for your comment :)
For now on, the grave at the bottom cannot be opened and will be used in a future version of the game.
Hi, looking at your screenshot I can see that you are in the park. In the park, there are only 2 items in the ground (although you can find more with the trees and bench later in the game). You need to go to the left of your screen to go back to the house and start digging in the garden. You'll find the others there.