- "[Spouse] and I have been thinking about having a baby..."
- — Mii, Tomodachi Life
A baby is an optional Mii exclusive to Tomodachi Life, created when two Miis successfully marry and, at a later time, decide that they would like to have a baby. Having babies is optional, but it is required in order to unlock certain features, such as child photos in the Photo Studio, and two of the rankings at the Rankings Board. However, babies won't be listed in the Town Hall's Mii List until their child stage, which rests at approximately 4-5 days old.
There is no limit as to how many babies can be born within a day to the island, but only one baby can be taken care of by a single family at a time. There is no restriction regarding how many babies can be born into a certain family, so a married couple may have had more children than there are apartments open.
Babies are first implemented in Tomodachi Life after being excluded in Tomodachi Collection, occurring when two sweethearts married and in good standing with each other, with both Miis being "Very happy" or better. At the start of the game, the player will be shown their Mii holding a baby, with a random Mii next to them, showing what may happen in the future. As the baby turns its head around, the screen fades to white.
Some time after a couple is married, one of the Miis will tell the player that they are thinking about having a baby, assuming that the Baby Option is enabled. Usually, these requests are given within eight days after their last child has left.
When the baby arrives and the player is overlooking the island, one of the parents will call the player and prompt them to their house. There, a music box melody plays as the two Miis await happily. The female Mii will be witnessed holding the newborn baby, wrapped in a blanket and wearing a bonnet, but with its back turned. After the wife tells the player they had a baby, they will be prompted to customize the baby:
- Are you hoping we had a boy or a girl? - The player can pick a gender - a boy or a girl - or have the game decide one at random. Upon answering, the baby's face is revealed, which is an obvious mix of the two parents' facial features. The baby utters a coo in return.
- How does he/she look? - The player can pick to keep the generated appearance, or edit the baby Mii's face. Editing the generated result is the only way a baby Mii's face can be modified until the baby becomes fully-grown.
- We like the name [Name], what do you think? - The player can have the parents use their own, random preferred name, think of another, or name the newborn him/herself. As with editing the face and personality, this cannot be changed again until the baby is grown up.
- What kind of personality do you think [he'll/she'll] have? - The player can make the baby share the personality of one of its parents, have it picked randomly, or define the personality themselves. The result, in combination with its gender, will determine the color scheme of the baby's clothes. Once picked, it may not be edited until the baby is fully grown.
After all the questions are asked, the mother will promise the player they will take good care of them, as the player is taken back to the island. Inside a Mii couple's house, the player can see the parents playing with their baby, or taking care of it. Each stage has different events which change from time to time. The only interactions that stay the same throughout all stages are the eating and sleeping scenes.
When visiting the married couple's house when they have a child, there is a "Babysitting" option next to "Visit". This activates a mini-game of sorts where the player either has to calm the baby down or play with them, depending on the stage.
When a baby is first born, at the baby and toddler stages, sometimes the player will randomly be called to assist the new parents who can't seem to calm the baby down. If the player tries and succeeds in calming the baby down, they will get a prize. If the player gives up, he/she will still get a prize for helping and the parent(s) will attempt to cheer up the baby. If the player is too hard with the baby, the parents will get angry and no prize will be won. The player can only get a prize if the parent(s) call for help.
Over the course of five days, the baby will grow from an infant, to a toddler, and then to a small child. When the child turns six days old, it will be a fully-grown child. Upon getting a call from one of the parents, the player will be taken to the couple's house, where the parents and fully grown child are waiting happily. The father announces that the baby has grown up, and asks if they should travel or move into the apartments.
Upon choosing, the player will have the option to make changes to the child's appearance and profile, and to give it a message to spread if the Mii is going to be a traveler. After this, the child will speak its first words, depending on which option chosen. The child's voice will be a randomized hybrid of its parents voices, which can be changed before they leave.
There is only one chance to decide if the child stays or goes, and the player cannot change their mind afterwards. If a child travels the world, they will only return for a short visit, and will never live on the island again. A child that stays on the island can be edited at any time, with the exception of their gender and age if they get in a relationship. If not enough room is present at the port or the apartments, the baby will revert to a stage 5 child.
At the end of the child's time growing up, the player will be rewarded with viewing a baby album and the end credits. These can be reviewed in the Town Hall after the child has grown up. A maximum of 50 albums can be held. Any album that the player wants to keep can be locked and kept forever. If a child living on the island or either one of it's parents is deleted, that child's album will be removed, even if it has been locked.
- If the player tends to a 2-3 day old baby while it is extremely happy (or the player sees the parent[s] playing peekaboo with the baby at 3-4 days old), the baby will laugh so hard it will fall to the side before righting itself back into a sitting position.
- If a newborn baby is left bald/with little hair, and/or the player said the baby looked fine, the baby will grow hair over the course of its childhood. The hairstyle will be randomly chosen from the all the hairstyles, but will most likely be from its gender's hairstyles. If selecting the bald hairstyle after the baby was born, it will continue to have no hair until it's grown up, then the player can change at will. This goes for any hairstyle.
- If the player changes a grown child's appearance, his/her past self in the Family Album will not reflect the new change. If the player edits a Mii after they have grown up, even if it was under the effects of Age-o-matic, their past self in the report or album will look the same as he/she does currently.
- When the camera zooms in on the baby after its face is revealed, if the player chooses to keep its appearance, the camera stays zoomed in until the personality question. If the player chooses to edit the baby's face, the camera zooms out to show the parents the rest of the way through.
- If the player chooses different head shape or hairstyle for the baby, it will keep it for the entirety of their time growing up.
- When a child reaches stage 5, it can talk like its parents, albeit with a high-pitched variation of the Miis' talking sound.
- If the baby is crying while the parents are playing peek-a-boo with it, all Miis present will be doing so instead of just the left Mii.
- If either one of the parents is sad or sick (either from a cold or stomach virus) on the day the child is born or has grown up, then the parents won't call the player until the player helps out the parent first.
- The same happens if either of the parents are in a fight with another Mii, and especially moments after that fight fails.
- If all houses currently have grown-up babies that can't leave their parents yet, then there's a possibility there won't be any problems, save for fights or wanting to play a game.