Citizenship and query for son turned 18 during process

I apologies for asking but I’m little bit confused regarding the ceremony.
On March 2021 I upload online all the documents for naturalisation. 4 persons. Me, my son of 17 years, my daughter of 16 years and my daughter of 8. I’ve been on checking on April the 10th and for the moment I received an email from MMST FMT saying that my son have to pay £80 for his ceremony because on April the 6th he done 18 years old.
For me and my 2 daughters didn’t came anything for the moment.
Maybe someone knows why?

Thank you very much.

Congratulations!
This is for your son only - if child turns 18 during the application processing he needs to attend the ceremony for which £80 is charged. The other children (under 18) don't need to attend the ceremony. For adults the ceremony fee is already paid as part of the application fee.