To register the children's holidays just:

  1. Select the Daily Routines icon
  2. Select the "Search" option
  3. Choose the child or Group and the date to mark as holidays
  4. Select the Entries button (the big one on top of the list of children)
  5. Choose the reason for the absence "Holidays
  6. Save

This way you can mark holidays for more than one child at the same time (by selecting the group instead of just one child).