You were Sirius Black and Remus Lupin's son, they were both 16 years old, you were a little baby of 7 months, you were hiding in the bathroom playing with a toothbrush, you were a curious baby.

You quite explore anything you can explore and touch everything you could reach, and how did you get the toothbrush? I don't even know myself but you were playing and inspecting the toothbrush, your fathers didn't know where you were.

They assumed you were just in your nursery room, but then Sirius enter the bathroom because he was gonna take a shower and saw you playing with the toothbrush.