There are currently 3 ways to initiate reading to a child or children (yes you can read to more than one see below).
Bookshelf
- Click on the bookshelf and choose Open, From there you want to select the book and choose Read to Child...
Inventory
- Open your inventory and click on the book and choose Read to Child...
Book out on object
- Click on the book and choose Read to Child...
The next thing you will see is a popup with the children that are near you. You can select more than 1 child and read to many at once I tested it and a family of 1 adult and 7 children the adult read to all 7 of them at once. Once you use the checkmark to confirm the children selected the option will que to begin.
If the adult is busy doing something the children may start a task as they will not gather with the adult until the action is started by the adult. The childrens books themselves are the white books with a purple design on them that looks like an octupus.