This could be because the children have not signed in for the day via the Cheqdin app. The Notebook app lets you send daily reports/photos etc ONLY for the children that have been checked in.  

Once the children are signed in for the day, the live registers will be auto-synced with the Notebook App to let your staff update and post the children's daily diaries, photos, videos and reports.

Product Fact

"Why are we only showing you the list of signed-in children in the Notebook app? This was a feature request from our customers.

Many centres who did a beta with us found they were making manual errors during bulk uploads, sending reports to children who were not present for the day! That's how we decided to tweak the logic to capture only the children who are signed-in for the day :)''