I haven't had many close calls like this for two reasons; 1) I've never had roommates, I've been fortunate enough to have been living on my own since the age of 19 and 2) many of the close friends I have already know, so I don't have to worry about the odd pacifier or onesie lying around the apartment when company comes a bit too early.
That being said, one friend who I didn't tell beforehand, nearly stumbled upon my little secret. One day I invited a friend over to help me move into my 2nd apartment. He lugged a big box of items up the stairs and opened my closet door to place the box in there. I didn't ask him to do that because my new bags of diapers were placed in the closet earlier that day, I also told him explicitly to just leave the box in the hallway, I did not tell him to find a place for it in my closet. I think he thought he was being helpful by taking initiative and putting that box away in the closet. Suffice it to say, I made no effort to cover up my recent delivery, the diaper bags were in plain sight and when I investigated, the box he placed in there was set neatly beside them. Fortunately though, I think he just placed he box in the closet without taking notice of what he set it beside, his mind was on helping me move, not perusing my personal items, he didn't mention a thing and when I finally decided to tell him about this side of myself a few weeks later he was none the wiser.
What I did during that instance was along the same lines of what has been suggested to you so far, I didn't bring it up, I treated the situation as though he saw nothing and surely enough, he never brought up the diapers, he truly didn't see anything and my stress and worry quickly faded away. I'd suggest you do the same, act naturally, chances are you covered yourself so quickly your roommate didn't notice a thing. Continue to act normal around your roommates and maybe be a bit more careful in the future i.e. ask them to knock next time, that's a simple courtesy or keep the door locked, you'll be fine
