The fact that nobody noticed the little girl slipping off through the corridors of the Starbase isn't that amazing for two reasons. The biggest reason is that Starbase 515 was an engineering station at Utopia Planitia. In fact, it is common knowledge that Utopia Planitia engineers are hell-bent on whatever their task is and that it often takes a red alert (or sometimes more than that) to jar their concentration away from their duties. As a result, all the officers that passed by Miral in the halls were either too lost in their own thoughts, too lost in the technical manual they were reading or too lost in the PADD they were working on to notice the four year old human-Klingon girl stalking the halls.
The second reason that it isn't surprising that Miral's presence in the hallways of a working Starbase went unnoticed is just because Miral Paris was quarter-Klingon. Centuries of instinct don't fade easily and something told the little girl that she should be stealthily creeping along the corridor wall, ducking behind every potted plant and through every hidden nook and cranny she could find. She had this sense that if her presence was known by the officers on the Deck that they'd be very unhappy with her and at the least send her back to the daycare center. However, since she still stubbornly held on to the thought that her mother would be overjoyed to see her, Miral kept stalking her way through the corridor until she found a turbolift.
Fortunately for her, unlike the nursery doors, the doors to the turbolift noticed her presence and she entered it without any problems. At this point it occurred to her that she didn't know where her mother worked on the Starbase, so she did what seemed to a four year old the most logical course of action. She asked the empty turbolift.
"'Scuse me, where does my mommy work?"
"Please restate parameters."
"My mommy! Where is she?"
"Please restate parameters. Specify name when requesting location."
Miral was catching on. "Where is my mommy, B'Elanna Torres?"
"Lt. Commander B'Elanna Torres-Paris is on Deck 15."
"Okay." Miral waited a minute for the turbolift to take her to her mommy. When nothing happened, she turned her attention back to the turbolift.
"Take me to my mommy, please," she asked in the sweetest voice she could muster.
"Please restate parameters."
Miral was now thoroughly frustrated with the obstinate turbolift, and so she now tried force. In her little voice she growled at the turbolift. "Take me to my mommy! NOW!" She paused for a moment's thought. "My mommy's on Deck 15. Take me to Deck 15!"
The turbolift finally took off towards its destination and after a moment, stopped at a deserted corridor.
"Thank you very much," Miral told the turbolift as she left it and skipped off down the hallway, entering in the first door she could find.