Click on Show Hidden in the Rolls Screen
If you see the child in Red, this means that they have been removed from the roll. To add them back on, remove the entry in Red then click on Count All to bring them back in pencil and Charge the roll.
If you see the child in Green, this means they have been marked and then removed from the roll. To add them back on, click on Roll Entry add button to manually put them back onto the roll.