In order to get this achievement, you must get the good ending by playing each mini game. I'd start in night 2. The first mini game you will play is "BBs Air Adventure". In order to unlock this mini game, you must look at cam 8 and press x. At the start, you will see 7 balloons. Get all 7, but don't immediately exit. Go all the way to the left "stair" and jump out of the box. You'll fall to the ground, so once you do, walk to the right until you see another box. When you see it, jump into the side of the box and collect the last balloon. The game will then take you back to your office.
The next game you'll play is called "Mangle's Quest". To activate this one, you'll go onto cam 7 and hold down the x button while pressing this sequence on the D-Pad (left and up, down and left, right and up, down and right). The game will then load. You must collect all of Mangle's body parts while also avoiding the man trying to get you. If he gets you, you must restart the minigame. After you get a few pieces, the exit door will pop up, but don't exit. Instead, continue onto the top right stair and jump through the box once more. You'll fall into a glitchy red area. Once you do, go to the left until you see some balloons. If you don't see them, play either BBs Air Adventure or Mangles Quest a couple times until you see the balloons. Once you get the balloons, jump up the balloons to get the cake. It'll then take you back to your office. Once back there, play BBs Air Adventure once more up until you exit the box. As you float down, there should be some balloons. Land on them, then follow the path until you see the crying child. Walk up to it, and it'll give him some cake. Once that happens, you'll again return to your office. Now complete night 2 as you normally would.
Now you should be on night 3. Once on night 3, go onto every camera (excluding 7 and 8) and hold LT and press X to collect the cupcakes in each room to activate "Chica's Party". Once there, go to the right and collect the 2 cupcakes. Then drop down, but don't go towards the crying kids. Instead, go to the farthest left stair and once again jump outside the box. Jump up the balloons to the grey crying kid. Once you do, Chica will give him cake and you'll return to the office. Now complete night 3.
Once you're at night 4, you're gonna face the front wall and enter this code (395248) by pressing the following buttons on the d-pad and x button (up and right, down and right, x, up, left, down). This might be glitchy, so press the buttons on the d-pad first, then press the x button to register it (excluding the number 5 though, since you just press the x button.). This should load the mini game "Stage01". In order to beat this, jump off the stage, then walk to the left. You should glitch out of the box. Fall to the bottom, then walk to the right until you see the exit door. You guessed it, don't exit the game, but instead, jump against the left side of the box in order to glitch onto the roof. Once on the roof, jump to the top left and glitch onto the roof of the next stage. Walk to the left half of the stage you're currently on, then jump up and glitch inside the stage right above you. Walk to the right side of the stage with the kids, then jump up the right wall onto the roof. Finally, jump to the top right and you'll glitch into a box with another grey crying kid. Walk towards him and you'll give him cake. Once you achieve this, you'll be sent back to your office. Now, you can complete night 4.
Now you should be on night 5. Face the right side of your office and spam X in order to return to the "Stage01" mini game, but this time, you'll be playing as Shadow Bonnie. To get to the next grey crying kid, press B until the background changes to "BBs Air Adventure". Just like in that game, go to the top left "stair" and jump out of the box. Fall to the ground, and press B until you spawn in the room with the kid. Once the kid gets its cake, you should return to your office. You are now at the final mini game. Go onto camera 3 and press RT and X to enter the game "Happiest Day". Walk all the way to the right until you see the last grey crying child. Walk up to it to give it cake, wait for the scene to finish, and then you'll return to your office. Now complete night 5.
The achievement should pop after the game ends.