This War of Mine: The Little Ones

For this achievement you need to bring a child up to Content in his/her happiness. Best way to go raise up his/her happiness is to talk with other members of the group, play during the day, sleep in a bed at night and avoid doing anything negative (stealing, killing, refusing to assist neighbors)

It will also help if you provide toys, or build a swing set, or complete any assist your neighbor missions. Happy Hunting!

It's actually pretty hard to set the achievements up, mainly because the game seems to do completely random things.

However, this actually turns out to be easy. Start a "Write your own story game" and create a game with three survivors, I chose one to be a child and grandparent as one of the survivors. This seems to give the child an moral boost straight away, as long as you keep both happy and healthy.

Eventually an assist event will spawn, send the third survivor to complete this, make sure granny is on 'guard duties' during the night and then build a swing after the night has passed. Whenever the child starts to get upset give them a turn on the swings, make sure to let them draw over the walls and what I also find helpful is if the third survivor has the 'Psychologist' background (you may have to create a brand new survivor)