Children
The player is able to have children after they upgraded their house to the third upgrade and are in a marriage. If the player is married to the same sex, you will be able to adopt children. You will be asked if you want to have a child in a higher chance when you go to bed before your spouse.
In the current version, you can only have two kids of different sex, that will not pass the Toddler stage. If your elder child has already make the crib empty, another child may be acquired soon.
Biological children
If you maintain a good relationship with your spouse (hearts maxed out) and already have the nursery, once again you can give your spouse the bouquet. It is a sign for him/her that your're ready for having a baby. If you go to bed he/she will ask whether you want a child. If the player agrees, after 14 days, a baby is born and put in the crib at nursery. After 14 days in the nursery, the baby is will stay sleeping. After this, it will be laying in the crib for another 14 days, but you can play with it. When this stage is passed, it will be released out of its crib and for another 14 days it will be crawling around in your house. Finally, the baby will be in the toddler stage for the rest of it's life. It will start using beds in the nursery.
Adopted children
Similar to how you would obtain a child biologically, adoption works in very much the same fashion. Maintain a good relationship with your spouse (of the same gender), have the nursery, and go to bed earlier than your spouse (usually before 10pm). Eventually, a prompt will appear asking if you would like to adopt a child. If the player agrees, the adoption should occur (probably within 14 days, as with biological child).
While you are waiting for your child, your spouse will tell you that they have filed the adoption paperwork.
Your child will appear in the middle of the night, with a note saying that the adoption agency dropped off your new baby.
Stages
Stage 1 (interaction with the child is not possible, it'll always say "your child is sleeping")
Stage 2 (when interacting with the child, the player will throw it into the air, which improves the relationship level)
Stage 3 (the child will crawl around the house and play with toys. Sometimes it might be buggy and get stuck in furniture. At night it will be put back into the crib automatically.)
Stage 4 (the child will walk around the house. Can right click on child to interact / increase heart level.)
