You won't be able to find the toy box this early in the chapter, there are more diary pages you have to find first.
have you interacted with the plant in the room where you found the second diary page? It gives you a hint on what to do next.
About the room at the top left of the house, this room will become accessable later on in the chapter.
The game was supposed to have some difficult puzzles in it, so I wouldn't want to make it easier, but I could write a walkthrough!
Also, thank you for playing the game and I'm really glad you're enjoying it!
Hello! I've completed writing the walkthrough. I hope I covered everything important! Here it is: https://yumekakaro.itch.io/breaking-dimensions/devlog/106501/walkthrough
Let me know if you have any more trouble!