There are two entrances to the empty room besides the chimney: the window and the door.
Assuming that Little Mew was smart enough to hold on to the key, the door most likely hasn't been unlocked.
Instead, what his father WAS able to do, is to open the window.
Problem with this theory is: while Papa Number is opening the window, there is no one besides Little Mew who could have eaten the cookies and drank the milk... on the other hand, in the story it does say that seconds passed and THEN he heard munching, so perhaps:
Papa Number opened the window from the inside.
Mama Junko handed over the fridge, which Papa Number laid down in the corner.
Because Papa Number must have superhuman abilities to eat multiple cookies and drink an entire glass of milk, I reckon:
Papa Number emptied the plate outside through the window which was still open, and locked it again after he had emptied the tray.
Also, seems obvious but I'll mention it either way: Mama Junko most likely turned off the power in the power room since she exited it whilst Little Mew left the room.
Assuming that Little Mew was smart enough to hold on to the key, the door most likely hasn't been unlocked.
Instead, what his father WAS able to do, is to open the window.
Problem with this theory is: while Papa Number is opening the window, there is no one besides Little Mew who could have eaten the cookies and drank the milk... on the other hand, in the story it does say that seconds passed and THEN he heard munching, so perhaps:
Papa Number opened the window from the inside.
Mama Junko handed over the fridge, which Papa Number laid down in the corner.
Because Papa Number must have superhuman abilities to eat multiple cookies and drink an entire glass of milk, I reckon:
Papa Number emptied the plate outside through the window which was still open, and locked it again after he had emptied the tray.
Also, seems obvious but I'll mention it either way: Mama Junko most likely turned off the power in the power room since she exited it whilst Little Mew left the room.